Compounds and liquid-crystalline medium

ABSTRACT

Compounds of formula I, and liquid-crystalline media, preferably having a nematic phase and negative dielectric anisotropy, comprising:
         a) one or more compounds of formula I       

     
       
         
         
             
             
         
       
         
         
           
             and one or more other compounds selected from: 
             b) one or more compounds of formula II 
           
         
       
    
     
       
         
         
             
             
         
       
         
         
           
             and/or 
             c) one or more compounds selected from compounds of formulae III-1 to III-4 and B 
           
         
       
    
     
       
         
         
             
             
         
       
     
     Use thereof in electro-optical displays, particularly in active-matrix displays based on the VA, ECB, PALC, FFS or IPS effect and use of compounds of formula I for stabilisation of liquid-crystalline media which comprise one or more compounds of formula II and/or one or more compounds selected from compounds of formulae III-1 to III-4 and B.

The present invention relates to novel compounds, in particular for use in liquid-crystal media, but also to the use of these liquid-crystal media in liquid-crystal displays, and to these liquid-crystal displays, particularly liquid-crystal displays which use the ECB (electrically controlled birefringence) effect with dielectrically negative liquid crystals in a homeotropic initial alignment. The liquid-crystal media according to the invention are distinguished by a particularly short response time in the displays according to the invention at the same time as a high voltage holding ratio (VHR or also just HR for short).

The principle of electrically controlled birefringence, the ECB effect or DAP (deformation of aligned phases) effect, was described for the first time in 1971 (M. F. Schieckel and K. Fahrenschon, “Deformation of nematic liquid crystals with vertical orientation in electrical fields”, Appl. Phys. Lett. 19 (1971), 3912). Papers by J. F. Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869) followed.

The papers by J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982), 244) have shown that liquid-crystalline phases must have high values for the ratio between the elastic constants K₃/K₁, high values for the optical anisotropy Δn and values for the dielectric anisotropy Δε of −0.5 in order to be suitable for use for high-information display elements based on the ECB effect. Electro-optical display elements based on the ECB effect have a homeotropic edge alignment (VA technology=vertically aligned or also VAN=vertical aligned nematic). Dielectrically negative liquid-crystal media can also be used in displays which use the so-called IPS (in-plane switching) effect.

Industrial application of this effect in electro-optical display elements requires LC phases which have to meet a multiplicity of requirements. Particularly important here are chemical resistance to moisture, air and physical influences, such as heat, radiation in the infrared, visible and ultraviolet regions, and direct and alternating electric fields.

Furthermore, LC phases which can be used industrially are required to have a liquid-crystalline mesophase in a suitable temperature range and low viscosity.

None of the series of compounds having a liquid-crystalline mesophase that have been disclosed hitherto includes a single compound which meets all these requirements. Mixtures of two to 25, preferably three to 18, compounds are therefore generally prepared in order to obtain substances which can be used as LC phases.

Matrix liquid-crystal displays (MLC displays) are known. Non-linear elements which can be used for individual switching of the individual pixels are, for example, active elements (i.e. transistors). The term “active matrix” is then used, where in general use is made of thin-film transistors (TFTs), which are generally arranged on a glass plate as substrate.

A distinction is made between two technologies: TFTs comprising compound semiconductors, such as, for example, CdSe, or TFTs based on polycrystalline and, inter alia, amorphous silicon. The latter technology currently has the greatest commercial importance worldwide.

The TFT matrix is applied to the inside of one glass plate of the display, while the other glass plate carries the transparent counterelectrode on its inside. Compared with the size of the pixel electrode, the TFT is very small and has virtually no adverse effect on the image. This technology can also be extended to fully colour-capable displays, in which a mosaic of red, green and blue filters is arranged in such a way that a filter element is located opposite each switchable pixel.

The TFT displays most used hitherto usually operate with crossed polarisers in transmission and are backlit. For TV applications, IPS cells or ECB (or VAN) cells are used, whereas monitors usually use IPS cells or TN (twisted nematic) cells, and notebooks, laptops and mobile applications usually use TN cells.

The term MLC displays here encompasses any matrix display having integrated non-linear elements, i.e., besides the active matrix, also displays with passive elements, such as varistors or diodes (MIM=metal-insulator-metal).

MLC displays of this type are particularly suitable for TV applications, monitors and notebooks or for displays with a high information density, for example in automobile manufacture or aircraft construction. Besides problems regarding the angle dependence of the contrast and the response times, difficulties also arise in MLC displays due to insufficiently high specific resistance of the liquid-crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, September 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, pp. 141 ff., Paris; STROMER, M., Proc. Eurodisplay 84, September 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, pp. 145 ff., Paris]. With decreasing resistance, the contrast of an MLC display deteriorates. Since the specific resistance of the liquid-crystal mixture generally drops over the life of an MLC display owing to interaction with the inside surfaces of the display, a high (initial) resistance is very important for displays that have to have acceptable resistance values over a long operating period.

Displays which use the ECB effect have become established as so-called VAN (vertically aligned nematic) displays, besides IPS displays (for example: Yeo, S. D., Paper 15.3: “An LC Display for the TV Application”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 758 and 759) and the long-known TN displays, as one of the three more recent types of liquid-crystal display that are currently the most important, in particular for television applications.

The most important designs which may be mentioned are: MVA (multidomain vertical alignment, for example: Yoshide, H. et al., Paper 3.1: “MVA LCD for Notebook or Mobile PCs . . . ”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book I, pp. 6 to 9, and Liu, C. T. et al., Paper 15.1: “A 46-inch TFT-LCD HDTV Technology . . . ”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 750 to 753), PVA (patterned vertical alignment, for example: Kim, Sang Soo, Paper 15.4: “Super PVA Sets New State-of-the-Art for LCD-TV”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 760 to 763) and ASV (advanced super view, for example: Shigeta, Mitzuhiro and Fukuoka, Hirofumi, Paper 15.2: “Development of High Quality LCDTV”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 754 to 757).

In general form, the technologies are compared, for example, in Souk, Jun, SID Seminar 2004, Seminar M-6: “Recent Advances in LCD Technology”, Seminar Lecture Notes, M-6/1 to M-6/26, and Miller, Ian, SID Seminar 2004, Seminar M-7: “LCD-Television”, Seminar Lecture Notes, M-7/1 to M-7/32. Although the response times of modern ECB displays have already been significantly improved by addressing methods with overdrive, for example: Kim, Hyeon Kyeong et al., Paper 9.1: “A 57-in. Wide UXGA TFT-LCD for HDTV Application”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book I, pp. 106 to 109, the achievement of video-compatible response times, in particular in the switching of grey shades, is still a problem which has not yet been solved to a satisfactory extent.

ECB displays, like ASV displays, use liquid-crystalline media having negative dielectric anisotropy (Δε), whereas TN and to date all conventional IPS displays use liquid-crystalline media having positive dielectric anisotropy.

In liquid-crystal displays of this type, the liquid crystals are used as dielectrics, whose optical properties change reversibly on application of an electrical voltage.

Since in displays in general, i.e. also in displays in accordance with these mentioned effects, the operating voltage should be as low as possible, use is made of liquid-crystal media which are generally predominantly composed of liquid-crystal compounds, all of which have the same sign of the dielectric anisotropy and have the highest possible value of the dielectric anisotropy. In general, at most relatively small proportions of neutral compounds and if possible no compounds having a sign of the dielectric anisotropy which is opposite to that of the medium are employed. In the case of liquid-crystal media having negative dielectric anisotropy for ECB displays, predominantly compounds having negative dielectric anisotropy are thus employed. The liquid-crystal media employed generally consist predominantly and usually even essentially of liquid-crystal compounds having negative dielectric anisotropy.

In the media used in accordance with the present application, at most significant amounts of dielectrically neutral liquid-crystal compounds and generally only very small amounts of dielectrically positive compounds or even none at all are typically employed, since in general the liquid-crystal displays are intended to have the lowest possible addressing voltages.

For many practical applications in liquid-crystal displays, the known liquid-crystal media are not sufficiently stable. In particular, their stability to irradiation with UV, but also even with conventional backlighting, results in an impairment, in particular, of the electrical properties. Thus, for example, the conductivity increases significantly.

The use of so-called “hindered amine light stabilisers”, HALS for short, has already been proposed for the stabilisation of liquid-crystal mixtures.

Nematic liquid-crystal mixtures having negative dielectric anisotropy which comprise a small amount of TINUVIN® 770, a compound of the formula

as stabilisers, are proposed, for example, in WO 2009/129911 A1 and in WO 2012/076105 A1. However, the corresponding liquid-crystal mixtures do not have adequate properties for some practical applications. Inter alia, they are not sufficiently stable to irradiation using typical CCFL (cold cathode fluorescent lamp) and in particular the typical, modern LED (light-emitting diode) backlighting.

Similar liquid-crystal mixtures are also known, for example, from EP 2 182 046 A1, WO 2008/009417 A1, WO 2009/021671 A1 and WO 2009/115186 A1. However, the use of stabilisers is not indicated therein.

According to the disclosure therein, these liquid-crystal mixtures may optionally also comprise stabilisers of various types, such as, for example, phenols and sterically hindered amines (hindered amine light stabilisers, HALS for short). However, these liquid-crystal mixtures are characterised by relatively high threshold voltages and by at best moderate stabilities. In particular, their voltage holding ratio drops after exposure. In addition, a yellowish discoloration often arises.

The use of various stabilisers in liquid-crystalline media is described, for example, in JP (S)55-023169 (A), JP (H)05-117324 (A), WO 02/18515 A1 and JP (H) 09-291282 (A).

EP 2 993 216 A1 proposes, inter alia, the compound of the formula

for the stabilisation of dielectrically positive liquid-crystal media.

WO 2009/129911 A1 proposes the compounds

besides several others as second stabilisers besides nitrogen heterocycles for the stabilisation of dielectrically negative liquid-crystal media.

EP 2 514 800 A2 proposes the use of compounds of the formulae

in which R¹¹, besides other meanings, may also be O^(•) or OH, but not H, for stabilisation purposes in liquid-crystal media. However, the chemical stability of these compounds with respect to hydrolysis and particularly their solubility in liquid-crystal media are in most cases inadequate for practical use.

WO 2016/146245 A1 proposes the compound of the formula

for stabilisation purposes in liquid-crystal media. This compound, and the compound

are also proposed in DE 2016 005 083 A1 for stabilisation purposes in liquid-crystal media. However, the chemical stability, particularly with respect to hydrolysis, and especially the solubility in liquid-crystal media in the case of these compounds is in most cases inadequate for practical use.

The ether-linked compounds of the formulae

are proposed in the as yet unpublished application DE 10 2016 009485.0 for use as stabilisers for liquid-crystal mixtures.

The liquid-crystal media of the prior art having correspondingly low addressing voltages have relatively low electrical resistance values or a low VHR and often result in undesired flicker and/or inadequate transmission in the displays. In addition, they are not sufficiently stable to heating and/or UV exposure, at least if they have correspondingly high polarity, as is necessary for low addressing voltages.

On the other hand, the addressing voltage of the displays of the prior art which have a high VHR is often too high, in particular for displays which are not connected directly or not continuously to the power supply network, such as, for example, displays for mobile applications.

In addition, the phase range of the liquid-crystal mixture must be sufficiently broad for the intended application of the display. Thus, the low-temperature storage stability in the cell and preferably in bulk at −30° C. should be 240 h or more.

The response times of the liquid-crystal media in the displays must be improved, i.e. reduced. This is particularly important for displays for television or multimedia applications. In order to improve the response times, it has repeatedly been proposed in the past to optimise the rotational viscosity of the liquid-crystal media (γ₁), i.e. to achieve media having the lowest possible rotational viscosity. However, the results achieved here are inadequate for many applications and therefore make it appear desirable to find further optimisation approaches.

Adequate stability of the media to extreme loads, in particular to UV exposure and heating, is very particularly important. This is particularly difficult with simultaneous optimisation of the rotational viscosity. In particular in the case of applications in displays in mobile equipment, such as, for example, mobile telephones, this may be crucial, since, in particular in the case of these devices, relatively low addressing frequencies are preferably used.

The disadvantage of the MLC displays disclosed hitherto is due to their comparatively low contrast, the relatively high viewing-angle dependence and the difficulty in producing grey shades in these displays, as well as their inadequate VHR and their inadequate lifetime.

There thus continues to be a great demand for MLC displays having very high specific resistance at the same time as a large working-temperature range, short response times and a low threshold voltage, with the aid of which various grey shades can be produced and which have, in particular, a good and stable VHR.

The invention has an object, for example, of providing MLC displays, not only for monitor and TV applications, but also for mobile telephones and navigation systems, which are based on the ECB effect, the IPS effect or on the FFS (fringe field switching) effect, as described in Lee, S. H., Lee, S. L. and Kim, H. Y. “Electro-optical characteristics and switching principle of nematic liquid crystal cell controlled by fringe-field switching”, Appl. Phys. Letts., Vol. 73, No. 20, pp. 2881-2883 (1998), do not have the disadvantages indicated above, or only do so to a lesser extent, and at the same time have very high specific resistance values. In particular, it must be ensured for mobile telephones and navigation systems that they also work at extremely high and extremely low temperatures.

Surprisingly, it has been found that it is possible to achieve liquid-crystal displays which have, in particular in FFS displays, a low threshold voltage with short response times and at the same time a sufficiently broad nematic phase, favourable, relatively low birefringence (Δn), good stability to decomposition by heating and by exposure to UV, good solubility and a stable, high VHR if use is made in these display elements of nematic liquid-crystal mixtures which comprise at least one compound of the formula I and in each case at least one compound of the formula II, preferably of the sub-formula II-1, and/or at least one compound selected from the group of the compounds of the formulae III-1 to III-4, preferably of the formula III-2, and/or of formula B.

Media of this type can be used, in particular, for electro-optical displays having active-matrix addressing based on the ECB effect and for IPS displays and for FFS displays.

The invention thus relates to a liquid-crystalline medium based on a mixture of polar compounds which comprises at least one compound of the formula I and at least one compound which contains one or more compounds of the formula II and preferably in addition one or more compounds selected from the group of the compounds of the formulae III-1 to III-4, and/or of the formula B.

The mixtures according to the invention exhibit very broad nematic phase ranges with clearing points 70° C., very favourable values for the capacitive threshold, relatively high values for the holding ratio and at the same time good low-temperature stabilities at −20° C. and −30° C., as well as very low rotational viscosities. The mixtures according to the invention are furthermore distinguished by a good ratio of clearing point and rotational viscosity and by a high negative dielectric anisotropy.

Surprisingly, it has now been found that it is possible to achieve liquid-crystalline media having a suitably high Δϑ, a suitable phase range and Δn which do not have the disadvantages of the prior-art materials, or at least only do so to a considerably reduced extent.

Surprisingly, it has been found here that the compounds of the formula I, even when used alone without additional heat stabilisers, result in considerable, in many cases adequate, stabilisation of liquid-crystal mixtures both to UV exposure and also to heating. This is the case, in particular, in most cases in which the parameter p in the compounds of the formula I used denotes 2 and n*p denotes 4, 6 or 8. In an embodiment of the present invention, the compounds of the formula I in which p denotes 2 and n denotes 2, 3 or 4 are therefore particularly preferred, and the use of precisely these compounds in the liquid-crystal mixtures according to the invention is particularly preferred. Preference is likewise given to the compounds of the formula I in which the group —Z¹¹—S¹¹—Z¹²— denotes ω-bisoxyalkylene, i.e. —O—S¹¹—O—.

However, adequate stabilisation of liquid-crystal mixtures both against UV exposure and against heating can also be achieved, in particular, if one or more further compounds, preferably phenolic stabilisers, are present in the liquid-crystal mixture in addition to the compound of the formula I, or the compounds of the formula I. These further compounds are suitable as heat stabilisers.

The invention thus relates to compounds of the formula I, and to a liquid-crystalline medium having a nematic phase and negative dielectric anisotropy which comprises one or more compounds of the formula I and one or more other compounds of the formula II and/or formulae III-1 to III-4 or formula B. Thus, the medium comprises:

-   a) one or more compounds of the formula I, preferably in a     concentration in the range from 1 ppm to 1500 ppm, preferably to     1000 ppm, preferably to 700 ppm, particularly preferably to 500 ppm,     more preferably in the range from 10 ppm to 400 ppm, particularly     preferably in the range from 20 ppm to 250 ppm,

in which

-   R¹¹ on each occurrence, independently of one another, denotes H, F,     a straight-chain or branched alkyl chain having 1-20 C atoms, in     which one —CH₂— group or, if present, a plurality of —CH₂— groups     may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups     cannot be replaced by —O—, and one or, if present, a plurality of     —CH₂— groups may be replaced by —CH═CH— or —C≡C—, and in which one H     atom or a plurality of H atoms may be replaced by F, OR¹³,     N(R¹³)(R¹⁴) or R¹⁵, -   R¹¹ preferably denotes H or alkyl, particularly preferably alkyl,     especially preferably n-alkyl and very particularly preferably     n-butyl, -   R¹² on each occurrence, independently of one another, denotes H, a     straight-chain or branched alkyl chain having 1-20 C atoms, in which     one —CH₂— group or a plurality of —CH₂— groups may be replaced by     —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by     —O—, a hydrocarbon radical which contains a cycloalkyl or     alkylcycloalkyl unit and in which one —CH₂— group or a plurality of     —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent     —CH₂— groups cannot be replaced by —O—, and in which one H atom or a     plurality of H atoms may be replaced by F, OR¹³, N(R¹³)(R¹⁴) or R¹⁵,     or an aromatic or heteroaromatic hydrocarbon radical, in which one H     atom or a plurality of H atoms may be replaced by F, OR¹³,     N(R¹³)(R¹⁴) or R¹⁵, -   R¹² preferably denotes H, unbranched alkyl or branched alkyl,     particularly preferably H or unbranched alkyl, -   R¹³ on each occurrence, independently of one another, denotes H, a     straight-chain or branched alkyl or acyl group having 1 to 10 C     atoms, preferably n-alkyl, or an aromatic hydrocarbon or carboxylic     acid radical having 6-12 C atoms, -   R¹⁴ on each occurrence, independently of one another, denotes H, a     straight-chain or branched alkyl or acyl group having 1 to 10 C     atoms, preferably n-alkyl, or an aromatic hydrocarbon or carboxylic     acid radical having 6-12 C atoms, preferably where R¹⁴ contains an     acyl group, -   R¹⁵ on each occurrence, independently of one another, denotes a     straight-chain or branched alkyl group having 1 to 10 C atoms, in     which one —CH₂— group or a plurality of —CH₂— groups may be replaced     by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced     by —O—, -   S¹¹ and S¹² on each occurrence, independently of one another, denote     an alkylene group having 1 to 20 C atoms, which is branched or,     preferably, straight-chain, preferably —(CH₂—)_(n) having 1-20 C     atoms, preferably having 1-10 C atoms, particularly preferably     having 1 to 6 C atoms, in which one —CH₂— group or, if present, a     plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two     adjacent —CH₂— groups cannot be replaced by —O—, and one or, if     present, a plurality of —CH₂— groups may be replaced by —CH═CH— or     —C≡C— and in which one H atom or a plurality of H atoms may be     replaced by F, OR¹³, N(R¹³)(R¹⁴) or R¹⁵, or denote a single bond, -   X¹¹ denotes C, -   Y¹¹ to Y¹⁴ each, independently of one another, denote methyl or     ethyl, particularly preferably all denote either methyl or ethyl and     very particularly preferably methyl, -   Z¹¹ to Z¹⁴ on each occurrence, independently of one another, denote     —O—, —(C═O)—, —O—(C═O)—, —(C═O)—O—, —O—(C═O)—O—, —(N—R¹³)—, or     —N—R¹³—(C═O)—, or may additionally be a single bond if S¹¹ is a     single bond, with the proviso that both Z¹¹ and Z¹² do not     simultaneously denote —O—, and, with the proviso that, if S¹² is a     single bond, both Z¹³ and Z¹⁴ do not simultaneously denote —O—, -   Z¹¹ preferably denotes —O—, -   Z¹³ preferably denotes a single bond, -   O^(•) denotes an oxide radical, -   p denotes 1 or 2, preferably 2, -   o denotes (3-p), and, -   if p is 2, -   n denotes an integer from 2 to 4, preferably 2 or 3, particularly     preferably 3, and -   m denotes (4-n), and, -   if p is 1, -   n denotes an integer from 3 to 10, preferably from 4 to 8,     particularly preferably 4 or 6, and -   m denotes (10-n), and

-    denotes an organic radical having (m+n) bonding sites, preferably     an alkanepolyyl unit having 1 to 30 C atoms, in which, in addition     to the m groups R¹² present in the molecule, but independently     thereof, a further H atom may be replaced by R¹² or a plurality of     further H atoms may be replaced by R¹², preferably an alkanetetrayl     unit having one or two valences on each of the terminal C atoms, in     which one —CH₂— group or a plurality of —CH₂— groups may be replaced     by —O— or —(C═O)— in such a way that two O atoms are not bonded     directly to one another, or a substituted or unsubstituted aromatic     or heteroaromatic hydrocarbon radical having up to 10 valences, in     which, in addition to the m groups R¹² present in the molecule, but     independently thereof, a further H atom may be replaced by R¹² or a     plurality of further H atoms may be replaced by R¹², -    and where, in the case where p=1, —X¹¹[—R¹¹]_(o)— may alternatively     also denote a single bond, -    and -   b) one or more compounds of the formula II

-   -   in which     -   R²¹ denotes an unsubstituted alkyl radical having 1 to 7 C atoms         or an unsubstituted alkenyl radical having 2 to 7 C atoms,         preferably an n-alkyl radical, particularly preferably having 3,         4 or 5 C atoms, and     -   R²² denotes an unsubstituted alkenyl radical having 2 to 7 C         atoms, preferably having 2, 3 or 4 C atoms, more preferably a         vinyl radical or a 1-propenyl radical and in particular a vinyl         radical,

-   and/or

-   c) one or more compounds selected from the group of the formulae     III-1 to III-4, preferably of the formula III-2, and formula B,

-   -   in which     -   R³¹ denotes an unsubstituted alkyl radical having 1 to 7 C         atoms, preferably an n-alkyl radical, particularly preferably         having 2 to 5 C atoms,     -   R³² denotes an unsubstituted alkyl radical having 1 to 7 C         atoms, preferably having 2 to 5 C atoms, or an unsubstituted         alkoxy radical having 1 to 6 C atoms, preferably having 2, 3 or         4 C atoms, and     -   m, n and o each, independently of one another, denote 0 or 1,     -   R^(B1) and R^(B2) each, independently of one another, denote an         unsubstituted alkyl radical, alkoxy radical, oxaalkyl radical or         alkoxyalkyl radical having 1 to 7 C atoms, or an alkenyl radical         or alkenyloxy radical having 2 to 7 C atoms, and     -   L^(B1) and L^(B2) each, independently of one another, denote F         or Cl, preferably F.

In the compounds of the formula I, the groups N(R¹³)(R¹⁴) may preferably also be primary or secondary amines.

Preference is given to the following embodiments, independently:

-   p is 2,

-    is an organic radical having 4 bonding sites, preferably an     alkanetetrayl unit having 1 to 30 C atoms, in which, in addition to     the m groups R¹² present in the molecule, but independently thereof,     a further H atom may be replaced by R¹² or a plurality of further H     atoms may be replaced by R¹², preferably an alkanetetrayl unit     having one or two valences on each of the two terminal C atoms, in     which one —CH₂— group or a plurality of —CH₂— groups may be replaced     by —O— or —(C═O)— in such a way that two O atoms are not bonded     directly to one another, or a substituted or unsubstituted aromatic     or heteroaromatic hydrocarbon radical having up to 8 valences, in     which, in addition to the m groups R¹² present in the molecule, but     independently thereof, a further H atom may be replaced by R¹² or a     plurality of further H atoms may be replaced by R¹²,

denotes

(biphenyl-1,1′,3,3′-tetrayl),

(benzene-1,2,4,5-tetrayl), >CH—[CH₂]_(r)—CH< (where r∈{0, 1, 2, 3, 4, 5 to 18}, —CH₂—(CH—)—[CH₂]_(q)—(CH—)—CH₂—< (where q∈{0, 1, 2, 3, 4, 5 to 16},

denotes

(benzene-1,3,5-triyl),

(benzene-1,2,4-triyl) or >CH—[CH₂]_(r)—CH₂— (where r is 0, 1, 2, 3, 4, 5 to 18) or

denotes —CH₂—[CH₂]_(r)—CH₂— (where r is 0, 1, 2, 3, 4, 5 to 18), octane-1,8-diyl, heptane-1,7-diyl, hexane-1,6-diyl, pentane-1,5-diyl, butane-1,4-diyl, propane-1,3-diyl, ethane-1,2-diyl, or

(1,4-phenylene),

(1,3-phenylene),

(1,2-phenylene) or

(1,4-cyclohexylene).

In the above and below embodiments where the ZG group has less than 4 groups bonded thereto, this means that there are a number of [R¹²]_(m)— groups being H which make up the proper total for m and n, i.e., where p=1, m+n=10 and where p=2, m+n=4,

In an alternative preferred embodiment,

p denotes 1.

In the present application, the elements all include their respective isotopes. In particular, one or more H in the compounds may be replaced by D, and this is also particularly preferred in some embodiments. A correspondingly high degree of deuteration of the corresponding compounds enables, for example, detection and recognition of the compounds. This is very helpful in some cases, in particular in the case of the compounds of the formula I.

In the present application,

-   alkyl particularly preferably denotes straight-chain alkyl, in     particular CH₃—, C₂H₅—, n-C₃H₇—, n-C₄H₉— or n-C₅H₁₁—, and -   alkenyl particularly preferably denotes CH₂═CH—, E-CH₃—CH═CH—,     CH₂═CH—CH₂—CH₂—, E-CH₃—CH═CH—CH₂—CH₂— or E-(n-C₃H₇)—CH═CH—.

The liquid-crystalline media in accordance with the present application preferably comprise in total 1 ppm to 2500 ppm, preferably 1 ppm to 1500 ppm, preferably 1 to 600 ppm, even more preferably 1 to 250 ppm, preferably to 200 ppm, and very particularly preferably 1 ppm to 100 ppm, of compounds of the formula I.

The term “acyl” above and below means alkylacyl, i.e., alkylcarbonyl.

In a preferred embodiment of the present invention, in the compounds of the formula I,

denotes

(biphenyl-1,1′,3,3′-tetrayl) or

(benzene-1,2,4,5-tetrayl)

denotes

(benzene-1,3,5-triyl) or

(benzene-1,2,4-triyl),

denotes —(CH₂-)₂, —(CH₂-)₃, —(CH₂-)₄, —(CH₂-)₅, —(CH₂—)₆, —(CH₂-)₇, —(CH₂-)₈, i.e.

-   -   ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl,         pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl,         octane-1,8-diyl,

(1,4-phenylene),

(1,3-phenylene),

(1,2-phenylene) or

(trans-1,4-cyclohexylene) and/or

-   -   —Z¹²—S¹¹—Z¹¹— on each occurrence, independently of one another,         denotes —O—, S¹¹—O—, —O—S¹¹—O—, —(C═O)—O—S¹¹—O—,         —O—(C═O)—S¹¹—O—, —O—(C═O)—S¹¹—(C═O)—O—, —O—S¹¹—(C═O)—O—,         —(C═O)—O—S¹¹—C, —(C═O)—O—S¹¹—O—(C═O)— or —(N—R¹³)—S¹¹—O—,         —(N—R¹³—C(═O)—S¹¹—(C═O)—O or a single bond, preferably —O—,         —S¹¹—O—, —O—S¹¹—O—, —(C═O)—O—S¹¹—O—, —O—(C═O)—S¹¹—O— or         —O—S¹¹—(C═O)—O—, and/or     -   R¹¹, if present, denotes alkyl, alkoxy or H, preferably H or         alkyl, and/or     -   R¹² denotes H, methyl, ethyl, propyl, isopropyl or 3-heptyl, or         cyclohexyl.     -   In a preferred embodiment of the present application, in the         compounds of the formula I,

-   -   denotes a group selected from the group of the formulae

-   -   In a preferred embodiment of the present application, in the         compounds of the formula I,

-   -   denotes a group selected from the group of the formulae

-   -   in a preferred embodiment of the present application, in the         compounds of the formula I in which p preferably denotes 1,

-   -   denotes

preferably —O—S¹¹—O—, —S¹¹—O— or —O—S¹¹—, particularly preferably —O—S¹¹—O— or —S¹¹—O—.

-   -   In a further preferred embodiment of the present application, in         the compounds of the formula I, the group

-   -   preferably denotes a group selected from the group of the         formulae

-   -   In a further preferred embodiment of the present application in         which p is 2, which may be identical to or different from those         described above, in the compounds of the formula I,

-   -   preferably denotes a group selected from the group of the         formulae

-   -   In a further preferred embodiment of the present invention,         which may be identical to or different from those described         above, in the compounds of the formula I, the group

-   -   on each occurrence, independently of one another, denotes

-   -   preferably

In a particularly preferred embodiment of the present invention, in the compounds of the formula I, all groups

present have the same meaning.

These compounds are highly suitable as stabilisers in liquid-crystal mixtures. In particular, they stabilise the VHR of the mixtures against UV exposure.

In a preferred embodiment of the present invention, the media according to the invention comprise in each case one or more compounds of the formula I selected from the group of the compounds of the formulae I-1 to I-8, preferably to I-6, preferably selected from the group of the compounds of the formulae I-1 to I-5, particularly preferably of the formulae I-2 and/or I-3 and/or I-4,

in which the parameters have the meanings indicated above under formula I.

In addition to the compounds of the formula I or the preferred sub-formulae thereof, the media in accordance with the present invention preferably comprise one or more dielectrically neutral compounds of the formula II in a total concentration in the range from 5% or more to 90% or less, preferably from 10% or more to 80% or less, particularly preferably from 20% or more to 70% or less.

The medium according to the invention preferably comprises one or more compounds selected from the group of the formulae III-1 to III-4 in a total concentration in the range from 10% or more to 80% or less, preferably from 15% or more to 70% or less, particularly preferably from 20% or more to 60% or less.

The medium according to the invention particularly preferably comprises

-   -   one or more compounds of the formula III-1 in a total         concentration in the range from 5% or more to 30% or less,     -   one or more compounds of the formula III-2 in a total         concentration in the range from 3% or more to 30% or less,     -   one or more compounds of the formula III-3 in a total         concentration in the range from 5% or more to 30% or less,     -   one or more compounds of the formula III-4 in a total         concentration in the range from 1% or more to 30% or less.

Preferred compounds of the formula II are the compounds selected from the group of the compounds of the formulae II-1 and II-2, preferably of the formula II-1,

in which

-   alkyl denotes an alkyl radical having 1 to 7 C atoms, preferably     having 2 to 5 C atoms, -   alkenyl denotes an alkenyl radical having 2 to 5 C atoms, preferably     having 2 to 4 C atoms, particularly preferably 2 C atoms, -   alkenyl′ denotes an alkenyl radical having 2 to 5 C atoms,     preferably having 2 to 4 C atoms, particularly preferably having 2     to 3 C atoms.

In a preferred embodiment of the present invention, the media according to the invention comprise one or more compounds of the formula B, preferably in a concentration of 1 to 20%, particularly preferably 2 to 15% and very particularly preferably 3 to 9%,

in which

-   R^(B1) and R^(B2) in each case, independently of one another, denote     an unsubstituted alkyl radical, alkoxy radical, oxaalkyl radical or     alkoxyalkyl radical having 1 to 7 C atoms, or an alkenyl radical or     alkenyloxy radical having 2 to 7 C atoms, preferably both denote an     alkoxy radical, and -   L^(B1) and L^(B2) in each case, independently of one another, denote     F or Cl, preferably F.

The media according to invention preferably comprise one or more compounds of the formula III-1, preferably one or more compounds selected from the group of the compounds of the formulae III-1-1 and III-1-2,

in which the parameters have the meanings given above in the case of formula III-1 and preferably

-   R³¹ denotes an alkyl radical having 2 to 5 C atoms, preferably     having 3 to 5 C atoms, and -   R³² denotes an alkyl or alkoxy radical having 2 to 5 C atoms,     preferably einen alkoxy radical having 2 to 4 C atoms, or an     alkenyloxy radical having 2 to 4 C atoms.

The media according to the invention preferably comprise one or more compounds of the formula III-2, preferably one or more compounds selected from the group of the compounds of the formulae III-2-1 and III-2-2,

in which the parameters have the meanings given above in the case of formula III-2 and preferably

-   R³¹ denotes an alkyl radical having 2 to 5 C atoms, preferably     having 3 to 5 C atoms, and -   R³² denotes an alkyl or alkoxy radical having 2 to 5 C atoms,     preferably an alkoxy radical having 2 to 4 C atoms, or an alkenyloxy     radical having 2 to 4 C atoms.

The media according to the invention preferably comprise one or more compounds of the formula III-3, preferably one or more compounds selected from the group of the compounds of the formulae III-3-1 and III-3-2,

in which the parameters have the meanings given above in the case of formula III-3, preferably

-   R³¹ denotes an alkyl radical having 2 to 5 C atoms, preferably     having 3 to 5 C atoms, and -   R³² denotes an alkyl or alkoxy radical having 2 to 5 C atoms,     preferably an alkoxy radical having 2 to 4 C atoms, or an alkenyloxy     radical having 2 to 4 C atoms.

In a preferred embodiment, the media according to the invention comprise one or more compounds of the formula II selected from the group of the compounds of the formulae II-1 and 11-2.

In a different preferred embodiment, the media according to the invention comprise no compounds of the formula II.

The media according to the invention preferably comprise the following compounds in the total concentrations indicated:

-   -   10-60% by weight of one or more compounds selected from the         group of the compounds of the formulae III-1 to III-4 and/or     -   30-80% by weight of one or more compounds of the formulae IV         and/or V,     -   where the total content of all compounds in the medium is 100%.

In a particularly preferred embodiment, the media according to the invention comprise one or more compounds selected from the group of the compounds of the formulae OH-1 to OH-6,

These compounds are highly suitable for the stabilisation of the media against thermal loads.

In another preferred embodiment of the present invention, in which the media according to the invention comprise, in particular, one or more compounds of the formula I in which p denotes 2 and n denotes 2, 3 or 4, preferably 2 or 3, particularly preferably 3, these media have excellent stability.

In a further preferred embodiment of the present invention, the media according to the invention comprise at least in each case one or more compounds of the formula I in which p denotes 1 and n denotes 3, 4, 5 or 6, preferably 4, and the groups —Z¹¹—S¹¹—Z¹²— denote ω-bisoxyalkylene, i.e. —O—S¹¹—O—, these media have excellent stability.

The present invention also relates to electro-optical displays or electro-optical components which contain liquid-crystalline media according to the invention. Preference is given to electro-optical displays which are based on the IPS, FFS, VA or ECB effect preferably on the IPS or FFS effect, and in particular those which are addressed by means of an active-matrix addressing device.

Accordingly, the present invention likewise relates to the use of a liquid-crystalline medium according to the invention in an electro-optical display or in an electro-optical component, and to a process for the preparation of the liquid-crystalline media according to the invention, characterised in that one or more compounds of the formula I are mixed with one or more compounds of the formula II, preferably with one or more compounds of the sub-formula II-1, and with one or more further compounds, preferably selected from the group of the compounds of the formulae III-1 to III-4 and IV and/or V.

In addition, the present invention relates to a process for the stabilisation of a liquid-crystalline medium which comprises one or more compounds of the formula II and one or more compounds selected from the group of the compounds of the formulae III-1 to III-4, characterised in that one or more compounds of the formula I are added to the medium.

In a further preferred embodiment, the medium comprises one or more compounds of the formula IV,

worin

-   R⁴¹ denotes alkyl having 1 to 7 C atoms, preferably having 2 to 5 C     atoms, and -   R⁴² denotes alkyl having 1 to 7 C atoms or alkoxy having 1 to 6 C     atoms, both preferably having 2 to 5 C atoms.

In a further preferred embodiment, the medium comprises one or more compounds of the formula IV, selected from the group of the compounds of the formulae IV-1 and IV-2,

in which

-   alkyl and alkyl′, independently of one another, denote alkyl having     1 to 7 C atoms, preferably having 2 to 5 C atoms, -   alkoxy denotes alkoxy having 1 to 5 C atoms, preferably having 2 to     4 C atoms.

In a further preferred embodiment, the medium comprises one or more compounds of the formula V,

in which

-   R⁵¹ and R⁵², independently of one another, have one of the meanings     given for R²¹ and R²² and preferably denote alkyl having 1 to 7 C     atoms, preferably n-alkyl, particularly preferably n-alkyl having 1     to 5 C atoms, alkoxy having 1 to 7 C atoms, preferably n-alkoxy,     particularly preferably n-alkoxy having 2 to 5 C atoms, alkoxyalkyl,     alkenyl or alkenyloxy having 2 to 7 C atoms, preferably having 2 to     4 C atoms, preferably alkenyloxy,

if present, in each case, independently of one another, denote

preferably

preferably

denotes

and, if present,

preferably denotes

-   Z⁵¹ to Z⁵³ each, independently of one another, denote —CH₂—CH₂—,     —CH₂—O—, —CH═CH—, —C≡C—, —COO— or a single bond, preferably     —CH₂—CH₂—, —CH₂—O— or a single bond and particularly preferably a     single bond, -   p and q each, independently of one another, denote 0 or 1, -   (p+q) preferably denotes 0 or 1.

In a further preferred embodiment, the medium comprises one or more compounds of the formula V selected from the group of the compounds of the formulae V-1 to V-10, preferably selected from the group of the compounds of the formulae V-1 to V-5,

in which the parameters have the meanings given above under formula V, and

-   Y⁵ denotes H or F, -   R⁵¹ denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to 7 C     atoms, and -   R⁵² denotes alkyl having 1 to 7 C atoms, alkenyl having 2 to 7 C     atoms or alkoxy having 1 to 6 C atoms, preferably alkyl or alkenyl,     particularly preferably alkenyl.

In a further preferred embodiment, the medium comprises one or more compounds of the formula V-1 selected from the group of the compounds of the formulae V-1a and V-1b, preferably of the formula V-1b,

in which

-   alkyl and alkyl′, independently of one another, denote alkyl having     1 to 7 C atoms, preferably having 2 to 5 C atoms, -   alkoxy denotes alkoxy having 1 to 5 C atoms, preferably having 2 to     4 C atoms.

In a further preferred embodiment, the medium comprises one or more compounds of the formula V-3 selected from the group of the compounds of the formulae V-3a and V-3b,

in which

-   alkyl and alkyl′, independently of one another, denote alkyl having     1 to 7 C atoms, preferably having 2 to 5 C atoms, and -   alkenyl denotes alkenyl having 2 to 7 C atoms, preferably having 2     to 5 C atoms.

In a further preferred embodiment, the medium comprises one or more compounds of the formula V-4 selected from the group of the compounds of the formulae V-4a and V-4b,

in which

-   alkyl and alkyl′, independently of one another, denote alkyl having     1 to 7 C atoms, preferably having 2 to 5 C atoms.

In a further preferred embodiment, the medium comprises one or more compounds of the formula III-4, preferably of the formula III-4-a,

in which

-   alkyl and alkyl′, independently of one another, denote alkyl having     1 to 7 C atoms, preferably having 2 to 5 C atoms.

The liquid-crystal media in accordance with the present invention may comprise one or more chiral compounds.

Particularly preferred embodiments of the present invention meet one or more of the following conditions,

where the acronyms (abbreviations) are explained in Tables A to C and illustrated by examples in Table D.

-   i. The liquid-crystalline medium has a birefringence of 0.060 or     more, particularly preferably 0.070 or more. -   ii. The liquid-crystalline medium has a birefringence of 0.130 or     less, particularly preferably 0.120 or less. -   iii. The liquid-crystalline medium has a birefringence in the range     from 0.090 or more to 0.120 or less. -   iv. The liquid-crystalline medium has a negative dielectric     anisotropy having a value of 2.0 or more, particularly preferably     3.0 or more. -   v. The liquid-crystalline medium has a negative dielectric     anisotropy having a value of 5.5 or less, particularly preferably     5.0 or less. -   vi. The liquid-crystalline medium has a negative dielectric     anisotropy having a value in the range from 3.6 or more to 5.2 or     less. -   vii. The liquid-crystalline medium comprises one or more     particularly preferred compounds of the formula II selected from the     sub-formulae given below:

-    in which alkyl has the meaning given above and preferably, in each     case independently of one another, denotes alkyl having 1 to 6,     preferably having 2 to 5, C atoms and particularly preferably     n-alkyl. -   viii. The total concentration of the compounds of the formula II in     the mixture as a whole is 25% or more, preferably 30% or more, and     is preferably in the range from 25% or more to 49% or less,     particularly preferably in the range from 29% or more to 47% or     less, and very particularly preferably in the range from 37% or more     to 44% or less. -   ix. The liquid-crystalline medium comprises one or more compounds of     the formula II selected from the group of the compounds of the     following formulae: CC-n-V and/or CC-n-Vm, particularly preferably     CC-3-V, preferably in a concentration of up to 50% or less,     particularly preferably up to 42% or less, and optionally     additionally CC-3-V1, preferably in a concentration of up to 15% or     less, and/or CC-4-V, preferably in a concentration of up to 20% or     less, particularly preferably up to 10% or less. -   x. The total concentration of the compounds of the formula CC-3-V in     the mixture as a whole is 20% or more, preferably 25% or more. -   xi. The proportion of compounds of the formulae III-1 to III-4 in     the mixture as a whole is 50% or more and preferably 75% or less. -   xii. The liquid-crystalline medium essentially consists of compounds     of the formulae I, II, III-1 to III-4, IV and V, preferably of     compounds of the formulae I, II and III-1 to III-4. -   xiii. The liquid-crystalline medium comprises one or more compounds     of the formula IV, preferably in a total concentration of 5% or     more, in particular 10% or more, and very particularly preferably     15% or more to 40% or less.

The invention furthermore relates to an electro-optical display having active-matrix addressing based on the VA or ECB effect, characterised in that it contains, as dielectric, a liquid-crystalline medium in accordance with the present invention.

The liquid-crystal mixture preferably has a nematic phase range having a width of at least 80 degrees and a flow viscosity ν₂₀ of at most 30 mm²·s⁻¹ at 20° C.

The liquid-crystal mixture according to the invention has a Δε of −0.5 to −8.0, in particular −1.5 to −6.0, and very particularly preferably −2.0 to −5.0, where Δε denotes the dielectric anisotropy.

The rotational viscosity γ₁ is preferably 150 mPa·s or less, in particular 120 mPa·s or less and very particularly preferably 120 mPa·s or less.

The mixtures according to the invention are suitable for all IPS and FFS-TFT applications. They are furthermore suitable for all VA applications, such as, for example, VAN, MVA, (S)-PVA and ASV applications, and PALC applications having negative Δε.

The nematic liquid-crystal mixtures in the displays according to the invention generally comprise two components A and B, which themselves consist of one or more individual compounds.

The liquid-crystalline media according to the invention preferably comprise 4 to 15, in particular 5 to 12, and particularly preferably 10 or less, compounds. These are preferably selected from the group of the compounds of the formulae I, II and III-1 to III-4, and/or IV and/or V.

The liquid-crystalline media according to the invention may optionally also comprise more than 18 compounds. In this case, they preferably comprise 18 to 25 compounds.

Besides compounds of the formulae I to V, other constituents may also be present, for example in an amount of up to 45%, but preferably up to 35%, in particular up to 10%, of the mixture as a whole.

The media according to the invention may optionally also comprise a dielectrically positive component, whose total concentration is preferably 10% or less, based on the entire medium.

In a preferred embodiment, the liquid-crystal media according to the invention comprise in total, based on the mixture as a whole,

100 ppm or more to 2500 ppm or less, preferably 300 ppm or more to 2000 ppm or less, particularly preferably 500 ppm or more to 1500 ppm or less and very particularly preferably 700 ppm or more to 1200 ppm or less, of the compound of the formula I, 20% or more to 60% or less, preferably 25% or more to 50% or less, particularly preferably 30% or more to 45% or less, of compounds of the formula II, and 50% or more to 70% or less of compounds of the formulae III-1 to III-4 and/or B.

In a preferred embodiment, the liquid-crystal media according to the invention comprise compounds selected from the group of the compounds of the formulae I, II, III-1 to III-4, IV and V, preferably selected from the group of the compounds of the formulae I, II and III-1 to III-4 and/or B; they preferably consist predominantly, particularly preferably essentially and very particularly preferably virtually completely of the compounds of these said formulae.

The liquid-crystal media according to the invention preferably have a nematic phase from in each case at least −20° C. or less to 70° C. or more, particularly preferably from −30° C. or less to 80° C. or more, very particularly preferably from −40° C. or less to 85° C. or more and most preferably from −40° C. or less to 90° C. or more.

The expression “have a nematic phase” here means on the one hand that no smectic phase and no crystallisation are observed at low temperatures at the corresponding temperature and on the other hand that no clearing occurs on heating out of the nematic phase. The investigation at low temperatures is carried out in a flow viscometer at the corresponding temperature and checked by storage in test cells having a cell thickness corresponding to the electro-optical application for at least 100 hours. If the storage stability at a temperature of −20° C. in a corresponding test cell is 1000 h or more, the medium is regarded as stable at this temperature. At temperatures of −30° C. and −40° C., the corresponding times are 500 h and 250 h respectively. At high temperatures, the clearing point is measured in capillaries by conventional methods. In addition, the shelf life at low temperatures in bulk (1 mL of sample) is determined in glass vials at temperatures of −20° C. or −30° C. At these temperatures, preferably at −30° C., the stable shelf lives are preferably 120 h or more, particularly preferably 240 h more.

In a preferred embodiment, the liquid-crystal media according to the invention are characterised by optical anisotropy values in the moderate to low range. The birefringence values are preferably in the range from 0.065 or more to 0.130 or less, particularly preferably in the range from 0.080 or more to 0.120 or less and very particularly preferably in the range from 0.085 or more to 0.110 or less.

In this embodiment, the liquid-crystal media according to the invention have negative dielectric anisotropy and relatively high absolute values of the dielectric anisotropy (|Δε|) which are preferably in the range from 2.7 or more to 5.3 or less, preferably to 4.5 or less, preferably from 2.9 or more to 4.5 or less, particularly preferably from 3.0 or more to 4.0 or less and very particularly preferably from 3.5 or more to 3.9 or less.

The liquid-crystal media according to the invention have relatively low values for the threshold voltage (V₀) in the range from 1.7 V or more to 2.5 V or less, preferably from 1.8 V or more to 2.4 V or less, particularly preferably from 1.9 V or more to 2.3 V or less and very particularly preferably from 1.95 V or more to 2.1 V or less.

In a further preferred embodiment, the liquid-crystal media according to the invention preferably have relatively low values of the average dielectric anisotropy (ε_(av.)≡(ε_(∥)+2ε_(⊥)/3) which are preferably in the range from 5.0 or more to 7.0 or less, preferably from 5.5 or more to 6.5 or less, still more preferably from 5.7 or more to 6.4 or less, particularly preferably from 5.8 or more to 6.2 or less and very particularly preferably from 5.9 or more to 6.1 or less.

In addition, the liquid-crystal media according to the invention have high values for the VHR in liquid-crystal cells.

In freshly filled cells at 20° C. in the cells, the VHR values are preferably greater than or equal to 95%, preferably greater than or equal to 97%, particularly preferably greater than or equal to 98% and very particularly preferably greater than or equal to 99%, and after 5 minutes in the oven at 100° C. in the cells, these are greater than or equal to 90%, preferably greater than or equal to 93%, particularly preferably greater than or equal to 96% and very particularly preferably greater than or equal to 98%.

In general, liquid-crystal media having a low addressing voltage or threshold voltage here have a lower VHR than those having a higher addressing voltage or threshold voltage, and vice versa.

These preferred values for the individual physical properties are preferably also in each case maintained by the media according to the invention in combination with one another.

In the present application, the term “compounds”, also written as “compound(s)”, means both one and also a plurality of compounds, unless explicitly indicated otherwise.

Unless indicated otherwise, the individual compounds are generally employed in the mixtures in concentrations in each case from 1% or more to 30% or less, preferably from 2% or more to 30% or less and particularly preferably from 3% or more to 16% or less.

In a preferred embodiment, the liquid-crystalline media according to the invention comprise

the compound of the formula I, one or more compounds of the formula II, preferably selected from the group of the compounds of the formulae CC-n-V and CC-n-Vm, preferably CC-3-V, CC-3-V1, CC-4-V and CC-5-V, particularly preferably selected from the group of the compounds CC-3-V, CC-3-V1 and CC-4-V, very particularly preferably the compound CC-3-V, and optionally additionally the compound(s) CC-4-V and/or CC-3-V1, one or more compounds of the formula III-1-1, preferably of the formula CY-n-Om, selected from the group of the compounds of the formulae CY-3-O2, CY-3-O4, CY-5-O2 and CY-5-O4, one or more compounds of the formula III-1-2, preferably selected from the group of the compounds of the formulae CCY-n-m and CCY-n-Om, preferably of the formula CCY-n-Om, preferably selected from the group of the compounds of the formulae CCY-3-O2, CCY-2-O2, CCY-3-O1, CCY-3-O3, CCY-4-O2, CCY-3-O2 and CCY-5-O2, optionally, preferably obligatorily, one or more compounds of the formula III-2-2, preferably of the formula CLY-n-Om, preferably selected from the group of the compounds of the formulae CLY-2-O4, CLY-3-O2, CLY-3-O3, one or more compounds of the formula III-3-2, preferably of the formula CPY-n-Om, preferably selected from the group of the compounds of the formulae CPY-2-O2 and CPY-3-O2, CPY-4-02 and CPY-5-02, one or more compounds of the formula III-4, preferably of the formula PYP-n-m, preferably selected from the group of the compounds of the formulae PYP-2-3 and PYP-2-4.

The compounds of the formula I according to the invention, or the compounds of the formula I to be employed in accordance with the invention, can advantageously be prepared in accordance with the following reaction schemes.

in which n preferably denotes 2, 3 or 4, particularly preferably 3 or 4.

In the reaction schemes above, Pg denotes a protecting group and Rg denotes a leaving group and the parameter n has the meaning given in the case of formula I, furthermore R¹ has the meanings given for R¹¹ in the case of formula I, the ring structure has the meanings given for ZG in the case of formula I, Sp¹ and Sp² have the meanings given for S¹ and S² respectively in the case of formula I, and preferably n denotes 3 or 4, the ring structure denotes an aromatic or aliphatic radical, Sp¹ and Sp² denote a single bond or an alkylene radical having 1 to 8 C atoms and R¹ denotes an alkyl radical having 1 to 8 C atoms.

For the present invention, the following definitions apply in connection with the specification of the constituents of the compositions, unless indicated otherwise in individual cases:

-   -   “comprise”: the concentration of the constituents in question in         the composition is preferably 5% or more, particularly         preferably 10% or more, very particularly preferably 20% or         more,     -   “predominantly consist of”: the concentration of the         constituents in question in the composition is preferably 50% or         more, particularly preferably 55% or more and very particularly         preferably 60% or more,     -   “essentially consist of”: the concentration of the constituents         in question in the composition is preferably 80% or more,         particularly preferably 90% or more and very particularly         preferably 95% or more, and     -   “virtually completely consist of”: the concentration of the         constituents in question in the composition is preferably 98% or         more, particularly preferably 99% or more and very particularly         preferably 100.0%.

This applies both to the media as compositions with their constituents, which can be components and compounds, and also to the components with their constituents, the compounds. Only in relation to the concentration of an individual compound relative to the medium as a whole does the term comprise mean: the concentration of the compound in question is preferably 1% or more, particularly preferably 2% or more, very particularly preferably 4% or more.

For the present invention, “≤” means less than or equal to, preferably less than, and “≥” means greater than or equal to, preferably greater than.

For the present invention,

denote trans-1,4-cyclohexylene, and

denote 1,4-phenylene.

For the present invention, the expression “dielectrically positive compounds” means compounds having a Δε of >1.5, the expression “dielectrically neutral compounds” means those where −1.5≤Δε≤1.5 and the expression “dielectrically negative compounds” means those where Δε<−1.5. The dielectric anisotropy of the compounds is determined here by dissolving 10% of the compounds in a liquid-crystalline host and determining the capacitance of the resultant mixture in each case in at least one test cell having a cell thickness of 20 μm with homeotropic and with homogeneous surface alignment at 1 kHz. The measurement voltage is typically 0.5 V to 1.0 V, but is always lower than the capacitive threshold of the respective liquid-crystal mixture investigated.

The host mixture used for dielectrically positive and dielectrically neutral compounds is ZLI-4792 and that used for dielectrically negative compounds is ZLI-2857, both from Merck KGaA, Germany. The values for the respective compounds to be investigated are obtained from the change in the dielectric constant of the host mixture after addition of the compound to be investigated and extrapolation to 100% of the compound employed.

The compound to be investigated is dissolved in the host mixture in an amount of 10%. If the solubility of the substance is too low for this purpose, the concentration is halved in steps until the investigation can be carried out at the desired temperature.

The liquid-crystal media according to the invention may, if necessary, also comprise further additives, such as, for example, stabilisers and/or pleochroic dyes and/or chiral dopants in the usual amounts. The amount of these additives employed is preferably in total 0% or more to 10% or less, based on the amount of the entire mixture, particularly preferably 0.1% or more to 6% or less. The concentration of the individual compounds employed is preferably 0.1% or more to 3% or less. The concentration of these and similar additives is generally not taken into account when specifying the concentrations and concentration ranges of the liquid-crystal compounds in the liquid-crystal media.

In a preferred embodiment, the liquid-crystal media according to the invention comprise a polymer precursor which comprises one or more reactive compounds, preferably reactive mesogens, and, if necessary, also further additives, such as, for example, polymerisation initiators and/or polymerisation moderators, in the usual amounts. The amount of these additives employed is in total 0% or more to 10% or less, based on the amount of the entire mixture, preferably 0.1% or more to 2% or less. The concentration of these and similar additives is not taken into account when specifying the concentrations and concentration ranges of the liquid-crystal compounds in the liquid-crystal media.

The compositions consist of a plurality of compounds, preferably 3 or more to 30 or fewer, particularly preferably 6 or more to 20 or fewer and very particularly preferably 10 or more to 16 or fewer compounds, which are mixed in a conventional manner. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent of the mixture. This is advantageously carried out at elevated temperature. If the selected temperature is above the clearing point of the principal constituent, completion of the dissolution operation is particularly easy to observe. However, it is also possible to prepare the liquid-crystal mixtures in other conventional ways, for example using pre-mixes or from a so-called “multibottle system”.

The mixtures according to the invention exhibit very broad nematic phase ranges having clearing points of 65° C. or more, very favourable values for the capacitive threshold, relatively high values for the holding ratio and at the same time very good low-temperature stabilities at −30° C. and −40° C. Furthermore, the mixtures according to the invention are distinguished by low rotational viscosities γ₁.

It goes without saying to the person skilled in the art that the media according to the invention for use in VA, IPS, FFS or PALC displays may also comprise compounds in which, for example, H, N, O, Cl, F have been replaced by the corresponding isotopes.

The structure of the liquid-crystal displays according to the invention corresponds to the usual geometry, as described, for example, in EP-A 0 240 379.

The liquid-crystal phases according to the invention can be modified by means of suitable additives in such a way that they can be employed in any type of, for example, ECB, VAN, IPS, GH or ASM-VA LCD display that has been disclosed to date.

Table E below indicates possible dopants which can be added to the mixtures according to the invention. If the mixtures comprise one or more dopants, it is (they are) employed in amounts of 0.01 to 4%, preferably 0.1 to 1.0%.

Stabilisers which can be added, for example, to the mixtures according to the invention, preferably in amounts of 0.01 to 6%, in particular 0.1 to 3%, are shown below in Table F.

For the purposes of the present invention, all concentrations are, unless explicitly noted otherwise, indicated in percent by weight and relate to the corresponding mixture or mixture component, unless explicitly indicated otherwise.

All temperature values indicated in the present application, such as, for example, the melting point T(C,N), the smectic (S) to nematic (N) phase transition T(S,N) and the clearing point T(N,I), are indicated in degrees Celsius (° C.) and all temperature differences are correspondingly indicated in differential degrees (° or degrees), unless explicitly indicated otherwise.

For the present invention, the term “threshold voltage” relates to the capacitive threshold (V₀), also known as the Freedericks threshold, unless explicitly indicated otherwise.

All physical properties are and have been determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, status November 1997, Merck KGaA, Germany, and apply for a temperature of 20° C., and Δn is determined at 589 nm and Δε at 1 kHz, unless explicitly indicated otherwise in each case.

The electro-optical properties, for example the threshold voltage (V₀) (capacitive measurement), are, as is the switching behaviour, determined in test cells produced at Merck Japan. The measurement cells have soda-lime glass substrates and are constructed in an ECB or VA configuration with polyimide alignment layers (SE-1211 with diluent **26 (mixing ratio 1:1), both from Nissan Chemicals, Japan), which have been rubbed perpendicularly to one another and effect homeotropic alignment of the liquid crystals. The surface area of the transparent, virtually square ITO electrodes is 1 cm².

Unless indicated otherwise, a chiral dopant is not added to the liquid-crystal mixtures used, but the latter are also particularly suitable for applications in which doping of this type is necessary.

The VHR is determined in test cells produced at Merck Japan. The measurement cells have soda-lime glass substrates and are constructed with polyimide alignment layers (for example AL-3046 from Japan Synthetic

Rubber, Japan, unless indicated otherwise) with a layer thickness of 50 nm or with the alignment layers described in the examples, which have been rubbed perpendicularly to one another. The layer thickness is a uniform 6.0 μm. The surface area of the transparent ITO electrodes is 1 cm².

The VHR is determined at 20° C. (VHR₂₀) and after 5 minutes in an oven at 100° C. (VHR₁₀₀) in a commercially available instrument from Autronic Melchers, Germany. The voltage used has a frequency of 60 Hz, or the conditions indicated in the examples.

The accuracy of the VHR measurement values depends on the respective value of the VHR. The accuracy decreases with decreasing values. The deviations generally observed in the case of values in the various magnitude ranges are compiled in their order of magnitude in the following table.

VHR range Deviation (relative) VHR values Δ_(G)VHR/VHR/% from to Approx. 99.6%   100%  +/−0.1 99.0%   99.6%   +/−0.2 98% 99% +/−0.3 95% 98% +/−0.5 90% 95% +/−1 80% 90% +/−2 60% 80% +/−4 40% 60% +/−8 20% 40% +/−10 10% 20% +/−20

The stability to UV irradiation is investigated in a “Suntest CPS”, a commercial instrument from Heraeus, Germany. The sealed test cells are irradiated for 2.0 hours without additional heating. The irradiation power in the wavelength range from 300 nm to 800 nm is 765 W/m² V, or the conditions indicated in the examples. A UV “cut-off” filter having an edge wavelength of 310 nm is used in order to simulate the so-called window glass mode. In each series of experiments, at least four test cells are investigated for each condition, and the respective results are indicated as averages of the corresponding individual measurements.

The decrease in the voltage holding ratio (ΔVHR) usually caused by the exposure, for example by UV irradiation by LCD backlighting, is determined in accordance with the following equation (1):

ΔVHR(t)=VHR(t)−VHR(t=0)  (1).

The relative stability (S_(rel)) of an LC mixture to a load for a time t is determined in accordance with the following equation, Equation (2):

$\begin{matrix} {{{S_{rel}(t)} = \frac{{{VHRref}\left( {t = 0} \right)} - {{VHRref}(t)}}{{{VHR}\left( {t = 0} \right)} - {{VHR}(t)}}},} & (2) \end{matrix}$

where “ref” stands for the corresponding unstabilised mixture.

A further characteristic quantity which, besides the VHR, can characterise the conductivity of the liquid-crystal mixtures is the ion density. High values of the ion density often result in the occurrence of display faults, such as image sticking and flickering. The ion density is preferably determined in test cells produced at Merck Japan Ltd. The test cells have substrates made from soda-lime glass and are designed with polyimide alignment layers (for example AL-3046 from Japan Synthetic Rubber, Japan, unless indicated otherwise) having a polyimide layer thickness of 40 nm. The layer thickness of the liquid-crystal mixture is a uniform 6.0 μm. The area of the circular, transparent ITO electrodes, which are additionally fitted with a guard ring, is 1 cm². The accuracy of the measurement method is about ±15%. The cells are dried overnight in an oven at 120° C. before filling with the relevant liquid-crystal mixture.

The ion density is measured using a commercially available instrument from TOYO, Japan. The measurement method is essentially a measure ment method which is analogous to cyclic voltammetry, as described in M. Inoue, “Recent Measurement of Liquid Crystal Material Characteristics”,

Proceedings IDW 2006, LCT-7-1, 647. In this method, an applied direct voltage is varied between a positive and negative maximum value in accordance with a pre-specified triangular profile. A complete run through the profile thus forms one measurement cycle. If the applied voltage is sufficiently large that the ions in the field are able to move to the respective electrode, an ion current forms due to discharge of the ions. The amount of charge transferred here is typically in the range from a few pC to a few nC. This makes highly sensitive detection necessary, which is ensured by the above-mentioned instrument. The results are depicted in a current/voltage curve. The ion current here is evident from the occurrence of a peak at voltages which are smaller than the threshold voltage of the liquid-crystal mixture. Integration of the peak area gives the value for the ion density of the mixture investigated. Four test cells are measured per mixture. The repetition frequency of the triangular voltage is 0.033 Hz, the measurement temperature is 60° C., the maximum voltage is ±3 V to ±10 V, depending on the magnitude of the dielectric anisotropy of the relevant mixture.

The rotational viscosity is determined using the rotating permanent magnet method and the flow viscosity in a modified Ubbelohde viscometer. For liquid-crystal mixtures ZLI-2293, ZLI-4792 and MLC-6608, all products from Merck KGaA, Darmstadt, Germany, the rotational viscosity values determined at 20° C. are 161 mPa·s, 133 mPa·s and 186 mPa·s respectively, and the flow viscosity values (ν) are 21 mm²·s⁻¹, 14 mm²·s⁻¹ and 27 mm²·s⁻¹ respectively.

The following symbols are used, unless explicitly indicated otherwise:

-   V₀ threshold voltage, capacitive [V] at 20° C., -   n_(e) extraordinary refractive index measured at 20° C. and 589 nm, -   n_(o) ordinary refractive index measured at 20° C. and 589 nm, -   Δn optical anisotropy measured at 20° C. and 589 nm, -   ε_(⊥) dielectric susceptibility perpendicular to the director at     20° C. and 1 kHz, -   ε_(∥) dielectric susceptibility parallel to the director at 20° C.     and 1 kHz, -   Δε dielectric anisotropy at 20° C. and 1 kHz, -   cl.p. or -   T(N,I) clearing point [° C.], -   ν flow viscosity measured at 20° C. [mm²·s⁻¹], -   γ₁ rotational viscosity measured at 20° C. [mPa·s], -   K₁ elastic constant, “splay” deformation at 20° C. [pN], -   K₂ elastic constant, “twist” deformation at 20° C. [pN], -   K₃ elastic constant, “bend” deformation at 20° C. [pN], and -   LTS low-temperature stability of the phase, determined in test     cells, -   VHR voltage holding ratio, -   ΔVHR decrease in the voltage holding ratio, -   S_(rel) relative stability of the VHR.

The following examples explain the present invention without limiting it. However, they show the person skilled in the art preferred mixture concepts with compounds preferably to be employed and the respective concentrations thereof and combinations thereof with one another. In addition, the examples illustrate the properties and property combinations that are accessible.

For the present invention and in the following examples, the structures of the liquid-crystal compounds are indicated by means of acronyms, with the transformation into chemical formulae taking place in accordance with

Tables A to C below. All radicals C_(n)H_(2n+1), C_(m)H_(2m+1) and C_(l)H_(2l+1) or C_(n)H_(2n), C_(m)H_(2m) and C_(l)H_(2l) are straight-chain alkyl radicals or alkylene radicals, in each case having n, m and I C atoms respectively. Table A shows the codes for the ring elements of the nuclei of the compound, Table B lists the bridging units, and Table C lists the meanings of the symbols for the left- and right-hand end groups of the molecules. The acronyms are composed of the codes for the ring elements with optional linking groups, followed by a first hyphen and the codes for the left-hand end group, and a second hyphen and the codes for the right-hand end group. Table D shows illustrative structures of compounds together with their respective abbreviations.

TABLE A Ring elements C

D

DI

A

AI

P

G

GI

U

UI

Y

P(F, Cl)Y

P(Cl,F)Y

np

n3f

nN3fI

th

thI

tH2f

tH2fI

o2f

o2f1

dh

B

K

KI

L

LI

F

FI

B

TABLE B Bridging units E —CH₂—CH₂— V —CH═CH— T —C≡C— W —CF₂—CF₂— B —CF═CF— Z —CO—O— ZI —O—CO— X —CF═CH— XI —CH═CF— O —CH₂—O— OI —O—CH₂— Q —CF₂—O— QI —O—CF₂—

TABLE C End groups On the left individually or in combination On the right individually or in combination -n- C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) -nO- C_(n)H_(2n+1)—O— -nO —O—C_(n)H_(2n+1) -V- CH₂═CH— -V —CH═CH₂ -nV- C_(n)H_(2n+1)—CH═CH— -nV —C_(n)H_(2n)—CH═CH₂ -Vn- CH₂═CH—C_(n)H_(2n)— -Vn —CH═CH—C_(n)H_(2n+1) -nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm —C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) -N- N≡C— -N —C≡N -S- S═C═N— -S —N═C═S -F- F— -F —F -CL- Cl— -CL —Cl -M- CFH₂— -M —CFH₂ -D- CF₂H— -D —CF₂H -T- CF₃— -T —CF₃ -MO- CFH₂O— -OM —OCFH₂ -DO- CF₂HO— -OD —OCF₂H -TO- CF₃O— -OT —OCF₃ -A- H—C≡C— -A —C≡C—H -nA- C_(n)H_(2n+1)—C≡C— -An —C≡C—C_(n)H_(2n+1) -NA- N≡C—C≡C— -AN —C≡C—C≡N On the left only in combination On the right only in combination - . . . n . . . - —C_(n)H_(2n)— - . . . n . . . —C_(n)H_(2n)— - . . . M . . . - —CFH— - . . . M . . . —CFH— - . . . D . . . - —CF₂— - . . . D . . . —CF₂— - . . . V . . . - —CH═CH— - . . . V . . . —CH═CH— - . . . Z . . . - —CO—O— - . . . Z . . . —CO—O— - . . . ZI . . . - —O—CO— - . . . ZI . . . —O—CO— - . . . K . . . - —CO— - . . . K . . . —CO— - . . . W . . . - —CF═CF— - . . . W . . . —CF═CF— in which n and m are each integers, and the three dots “ . . . ” are placeholders for other abbreviations from this table.

Besides the compounds of the formula I, the mixtures according to the invention preferably comprise one or more compounds of the compounds mentioned below.

The following abbreviations are used:

(n, m and z are, independently of one another, each an integer, preferably 1 to 6)

TABLE D

CC-n-m

CC-n-Om

CC-n-V

CC-n-Vm

CC-n-mV

CC-n-mVI

CC-V-V

CC-V-mV

CC-V-Vm

CC-Vn-mV

CC-nV-mV

CC-nV-Vm

CP-n-m

CP-n-Om

CCP-n-m

CCP-n-Om

CCP-V-m

CCP-nV-m

CCP-Vn-m

CCP-nVm-I

CPP-n-m

CGP-n-m

PGP-n-m

PGP-n-mV

PGP-n-mVI

CCZPC-n-m

CPPC-n-m

CGPC-n-m

CPGP-n-m

CY-n-m

CY-n-Om

CVY-n-m

CZY-n-Om

PY-n-m

PY-n-Om

CCY-n-m

CCY-n-Om

CCY-n-mOI

CCZY-n-Om

CPY-n-m

CPY-n-Om

PYP-n-m

CP(F,Cl)-n-Om

CLY-n-m

CLY-n-Om

CK-n-F

B-n-m

B-n-IV

B-Vn-IV

B-n-Om

B-n-OIV

B-nO-Om

PPGU-n

Table E shows chiral dopants which are preferably employed in the mixtures according to the invention.

TABLE E

C15

CB 15

CM 21

R-811/S-811

CM 44

CM 45

CM 47

CN

R-1011/S-1011

R-2011/S-2011

R-3011/S-3011

R-4011/S-4011

R-5011/S-5011

In a preferred embodiment of the present invention, the media according to the invention comprise one or more compounds selected from the group of the compounds from Table E.

Table F shows stabilisers which can preferably be employed in the mixtures according to the invention in addition to the compounds of the formula I. The parameter n here denotes an integer in the range from 1 to 12. In particular, the phenol derivatives shown can be employed as additional stabilisers since they act as antioxidants.

TABLE F

In a preferred embodiment of the present invention, the media according to the invention comprise one or more compounds selected from the group of the compounds from Table F, in particular one or more compounds selected from the group of the compounds of the two formulae

EXAMPLES

The following examples explain the present invention without restricting it in any way. However, the physical properties make it clear to the person skilled in the art what properties can be achieved and in what ranges they can be modified. In particular, the combination of the various properties which can preferably be achieved is thus well defined for the person skilled in the art.

Substance Examples

The following substances are preferred substances of the formula I in accordance with the present application or substances of the formula I preferably to be employed in accordance with the present application.

The following examples explain the present invention without limiting it in any way. However, the physical properties make it clear to the person skilled in the art which properties are to be achieved and in what ranges they can be modified. In particular, the combination of the various properties which can preferably be achieved is thus well defined for the person skilled in the art.

Synthesis Example 1: Synthesis of bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-{3-[2,5-bis({4-butyl-5-[(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]-4-{[(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]carbonyl}-5-oxopentyl})phenyl]propyl}-2-butylpropanedioate 1 Substance Example 1

Step 1.1: Synthesis of 3-[3,4-bis(3-hydroxypropyl)phenyl]propan-1-ol A

51.34 g (484.0 mmol) of anhydrous sodium carbonate are dissolved in 171.7 ml of water. A solution of 25.0 g (79.0 mmol) of 1,2,4-tribromobenzene and 67.7 g (476 mmol) of 2-butoxy-1,2-oxaborolane in 965.2 ml of tetrahydrofuran (THF) is added, 1.65 ml (11.9 mmol) of triethylamine are added, and the mixture is stirred and degassed for 30 min. using a stream of argon. 1.40 g (7.49 mmol) of palladium(II) chloride (59% of palladium, anhydrous) and 1.85 g (3.97 mmol) of 2-dicyclohexylphoshino-2′,6′-diisopropoxy-1,1′-biphenyl are added, and the reaction mixture is stirred under reflux for 18 hours. The reaction mixture is allowed to cool to room temperature (RT), water and methyl tertiary-butyl ether (MTBE) are added, and the phases are separated. The water phase is extracted with MTBE, and the combined organic phases are washed with saturated NaCl solution, dried over sodium sulfate, filtered and evaporated in vacuo. The product is obtained as a yellowish oil and is filtered through silica gel with a mixture of ethyl acetate (EA) and methanol (9:1). The product fractions are combined and evaporated in vacuo, giving the reaction product as a pale-yellow oil. The product is characterised by means of NMR spectroscopy.

¹H NMR (500 MHz, DMSO-d6)

δ=1.66 (m_(c), 6H, CH₂), 2.42-2.69 (m_((superimposed with DMSO)), 6H, CH₂,), 3.36-3.49 (m, 6H, CH₂), 4.44 (t, J=5.15 Hz, 1H), 4.48 (m_(c), 2H), 6.92 (dd, J=1.7, 7.72 Hz, 1H), 6.95 (d, J=1.53 Hz, 1H), 7.03 (d, J=7.7 Hz, 1H).

Step 1.2: Synthesis of 1,2,4-tris(3-iodopropyl)benzene B

30.2 ml (138 mmol) of triphenylphosphine are dissolved in 513 ml of acetonitrile, and a solution of 34.92 g (138.0 mmol) of iodine in 513 ml of acetonitrile is added dropwise with gentle cooling. An orange suspension forms during this addition. When the addition is complete, the mixture is stirred for a further 10 min. 13.3 g (197 mmol) of imidazole are added, and a solution of 10.0 g (39.3 mmol) of triol A in 100 ml of acetonitrile is subsequently added dropwise (a clear, yellow solution forms during this addition). The reaction solution is stirred at RT for 3 hours (h) and carefully poured into a cold sodium thiosulfate solution (decolouration occurs), and heptane is added. After washing by stirring, the phases are separated, the water phase is extracted with heptane, and the combined organic phases are washed with water, dried over sodium sulfate, filtered and evaporated in vacuo. The crude product is filtered through silica gel with heptane (H) and ethyl acetate (8:2), and evaporation of the product fractions gives the product as a colourless oil. The product is characterised by means of mass spectrometry.

MS (EI)=582.0

Step 1.3: Synthesis of 2-butylpropanedioyl Dichloride C

76.00 g (474.5 mmol) of 2-butylmalonic acid are initially introduced in the reaction apparatus and warmed to 40° C. 90.00 ml (1.240 mol) of thionyl chloride are then added dropwise over the course of about 30 min. (care, evolution of gas), and the mixture is stirred at room temperature (RT) for a further 5 hours (h). The evolution of gas decreases significantly within this time span. The reaction solution is then stirred at 50° C. for 18 h and subsequently at 70° C. for 5 h. On each increase in temperature, slight evolution of gas re-occurs. The reaction mixture is then cooled to room temperature and taken up in 300 ml of dry toluene, and excess thionyl chloride is separated off by distillation together with the toluene (8 mbar and RT to max. bath temperature of 80° C.), giving the crude product as a brownish liquid, which can be employed directly in the next synthesis step.

Step 1.4: Synthesis of bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-butylpropanedioate D

45.3 g (262.9 mmol) of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (free radical) and 40.1 ml (289.15 mmol) of triethylamine are dissolved in 419 ml of dichloromethane (DCM) and cooled to −11° C. A solution of 25.9 g (131.4 mmol) of the acid chloride C in 252 ml of DCM is then added dropwise at −11° C. to −6° C. over the course of 1.5 hours (h). The reaction mixture is stirred at max. 0° C. for about 3 h, slowly thawed and stirred at room temperature (RT) for 18 h. Saturated NaHCO₃ solution is added at 3-6° C. with cooling, the mixture is stirred briefly, and the phases are separated. The water phase is extracted with DCM, and the organic phases are combined, washed with saturated NaCl solution, dried over sodium sulfate, filtered and evaporated in vacuo. The crude product obtained (orange solid) is filtered through silica gel with DCM/MTBE (9:1), and the product fractions are evaporated in vacuo, giving the product as orange crystals.

Step 1.5: Synthesis of bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-{3-[2,5-bis({4-butyl-5-[(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]-4-{[(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]carbonyl}-5-oxopentyl})phenyl]propyl}-2-butylpropanedioate 1

0.31 g (7.80 mmol) of sodium hydride (60% suspension in paraffin oil) is suspended in 9.7 ml of N,N-dimethylformamide (DMF). 3.75 g (7.87 mmol) of a solution of the bisradical D dissolved in 29.0 ml DMF are added dropwise with gentle cooling (evolution of gas), and the mixture is stirred at RT for 1 hour. 1.40 g (2.39 mmol) of trisiodide B are added dropwise to the reaction solution (5° C. evolution of heat over 5 minutes), and the mixture is stirred at RT for 3 h. The reaction mixture is carefully added to ammonium chloride solution and extracted with MTBE. The phases are separated, the water phase is extracted with MTBE, washed with saturated NaCl solution, dried over sodium sulfate, filtered and evaporated in vacuo. The orange crude product obtained is filtered through silica gel with ethyl acetate/heptane (1:1), and the product fractions are evaporated in vacuo, giving the product as an orange solid which foams up in a glass-like manner. The product has the following properties.

Phases: glass transition temperature (TG)=23.5° C., decomposition from 150° C.

MS (APCI)=1605.1 [M+H⁺].

Synthesis Example 2: Synthesis of bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-(3-{3,5-bis[({4-butyl-5-[(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]-4-{[(1-oxy-2,2,6,6-tetramethylpiperidin-4-yl)oxy]carbonyl}-5-oxopentyl}oxy)carbonyl]benzoyloxy}propyl)-2-butylpropanedioate 2

Step 2.1: Synthesis of bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-butyl-2-[3-(oxan-2-yloxy)propyl]propanedioate E

3.20 g (80.4 mmol) of sodium hydride (60% suspension in paraffin oil) are suspended in 30 ml of DMF. A solution of 32.40 g (69.14 mmol) of bisradical D (from the synthesis of compound 1) in 300 ml of DMF is added dropwise to the reaction solution with gentle cooling (evolution of gas), and the mixture is stirred at RT for 1 h. A solution of 19.0 g (85.16 mmol) of 2-(3-bromopropoxy)tetrahydropyran in 200 ml of DMF is then added dropwise at RT (0.5° C. evolution of heat). For degassing of the reaction mixture before an increase in temperature, a gentle stream of argon is passed through the reaction mixture by means of an immersed Pasteur pipette for 30 minutes, and the mixture is subsequently stirred at 35° C. for 18 h. The reaction solution is allowed to cool to RT, added to saturated NaCl solution and extracted with MTBE, and the phases are separated. The aqueous phase is extracted with MTBE, and the organic phases are combined, washed with saturated NaCl solution, dried over sodium sulfate, filtered and evaporated in vacuo, giving the crude product as a red oil, which, for purification, is filtered through silica gel with DCM/MTBE (9:1), giving the product as a red oil.

Step 2.2: Synthesis of bis(1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl) 2-butyl-2-(3-hydroxypropyl)propanedioate F

36.5 g (56.1 mmol) of bisradical E and 9.50 g (55.2 mmol) of toluene-4-sulfonic acid monohydrate are dissolved in a mixture of 500 ml of methanol and 50 ml of water, and the mixture is stirred at 40° C. for 5 h. The reaction solution is cooled to RT and adjusted to pH=9 using NaHCO₃ solution with cooling and evaporated in vacuo. The aqueous residue is extracted with MTBE, and the combined organic phases are washed with saturated NaCl solution, dried over sodium sulfate, filtered and evaporated in vacuo, giving a red oil, which is dissolved in 250 ml of DCM, 6.00 g (55.6 mmol) of MnO₂ are added, and the mixture is stirred at RT for 1 h. (In the case of removal of the THP protecting group, the free radical is in some cases also converted into the OH compound, which is reversed using MnO₂). The reaction mixture is filtered through silica gel with DCM and evaporated in vacuo. The crude product obtained is filtered through silica gel with DCM/MTBE (7:3), and the product fractions are evaporated in vacuo to give a red oil.

Step 2.3: Synthesis of bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-(3-{3,5-bis[({4-butyl-5-[(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]-4-{[(1-oxy-2,2,6,6-tetramethylpiperidin-4-yl)oxy]carbonyl}-5-oxopentyl}oxy)carbonyl]-benzoyloxy}propyl)-2-butylpropanedioate 2

6.70 g (11.7 mmol of F and 50.0 mg (0.41 mmol) of 4-(dimethylamino)pyridine are dissolved in 100 ml of dichloromethane at RT, and the mixture is cooled to 4° C. 5.00 ml (36.1 mmol) of triethylamine are then added, and a solution of 1.00 g (3.77 mmol) of 1,3,5-benzenetricarbonyl chloride in 10 ml of DCM is subsequently added dropwise at 3-4° C. When the evolution of heat is complete, the mixture is allowed to warm to RT and is subsequently stirred at RT for 18 h. Ammonium chloride solution is then added with cooling, the mixture is stirred briefly, the phases are separated, and the aqueous phase is extracted with DCM. The combined organic phases are washed with dilute NaCl solution (better phase separation), dried over sodium sulfate, filtered and evaporated in vacuo, giving the reaction product as a red, solidifying foam. For further purification, the product is filtered through silica gel with DCM/MTBE (9:1 to 85:15), and the product fractions are evaporated in vacuo. The reaction product obtained is a red, solidifying foam. It has the following properties.

Phases: T_(g) (glass transition temperature) 52° C., C (melting point) 57° C. I, decomposition >175° C.

MS (APCI)=1734.

The following compounds are prepared analogously to the synthesis sequence(s) described.

Substance/Synthesis Example 3

Phases: T_(g) (glass transition temperature) −3° C. I (isotropic), decomposition >100° C.

Substance/Synthesis Example 4

Phases: T_(g) (glass transition temperature) 5° C. I (isotropic), decomposition >180° C.

Substance/Synthesis Example 5

Phases: T_(g) (glass transition temperature) 5° C. I (isotropic), decomposition >170° C.

Substance/Synthesis Example 6

Phases: T_(g) (glass transition temperature) 27° C. I (isotropic).

Substance/Synthesis Example 7

Substance/Synthesis Example 8

Phases: T_(g) (glass transition temperature) −3° C. I (isotropic).

Substance/Synthesis Example 9

Mixture Examples

Liquid-crystal mixtures having the compositions and properties as indicated in the following tables are prepared and investigated. The improved stability of the mixtures comprising compounds of the formula I is shown by comparison with unstabilised base mixtures as reference (Ref.).

Examples 1.1 to 1.3 and Corresponding Comparative Examples

Mixture (M-1) below is prepared and investigated.

Mixture M-1 Composition Compound Concentration No. Abbreviation /% by weight 1 CPP-3-2 4.5 2 CC-3-V 23.5 3 CCH-301 4.0 4 CCY-3-O2 4.0 5 CCY-3-O3 7.0 6 CCY-4-O2 8.0 7 CLY-3-O2 8.0 8 CPY-2-O2 7.0 9 CPY-3-O2 11.0 10 CY-3-O2 11.0 11 PY-3-O2 12.0 Σ 100.0 Physical properties T(N, I) = 86° C. n_(e)(20° C., 589 nm) = 1.5962 Δn(20° C., 589 nm) = 0.1118 ε_(⊥)(20°, 1 kHz) = 8.0 Δε(20°, 1 kHz) = −4.3 γ₁(20° C.) = 143 mPa · s k₁₁(20° C.) = 15.0 pN K₂₂(20° C.) = t.b.d. pN k₃₃(20° C.) = 16.7 pN V₀(20° C.) = 2.08 V Note: Here, as throughout the present application, t.b.d. means to be determined, unless indicated otherwise.

Firstly, the stability of the voltage holding ratio of mixture (M-1) itself is determined. The stability of mixture M-1 to irradiation with a backlight is investigated in a test cell having an alignment material for planar alignment, with a layer thickness of 6.0 μm and flat ITO electrodes. To this end, the mixture is, or the mixtures are, subjected to a test for exposure to a backlight. To this end, the stability of the corresponding test cells to illumination with an LED (light-emitting diode) backlight for LCDs is investigated. To this end, corresponding test cells are filled and sealed. These cells are then exposed to illumination with a commercial LCD backlight for various times (168 h, 336 h, 500 h and 1000 h). There is no additional heating besides the heat generated by the backlight. The “voltage holding ratio” is then in each case determined after 5 minutes at a temperature of 100° C. The results are compiled in the following table, Table 1a.

Here, as below, six test cells are filled and investigated for each individual mixture. The values indicated are the average of the six individual values.

The relative deviations of the “voltage holding ratio” values in various measurement series are typically in the range from about 3 to 4%.

100 ppm of the reference compounds R-1 to R-3

are added to each of three further parts of mixture M-1, and 100 ppm of in each case one of the three compounds I-1 to 1-3

are added to each of three further parts of mixture M-1, and the stability of the resultant mixtures (C-1.1, C-1.2 and C-1.3, as well as M-1.1, M-1.2 and M-1.3) is investigated as described above. The results are shown in the tables below, Tables 1a to 1d.

TABLE 1a VHR(t)/% @ c(stab.) 100° C., 60 Hz Ex. Mixture Stabiliser /ppm t = 0 h t = 168 h t = 336 h (Ref.) M-1 none 0 80.4 59.1 58.2 C1.1 C-1-1 R-1 100 t.b.d. t.b.d. t.b.d. C1.2 C-1-2 R-2 100 74.1 66.8 66.6 C1.3 C-1-3 R-3 100 73.1 73.0 72.4 M1.1 M-1-1 I-1 100 72.6 74.9 74.0 M1.2 M-1-2 I-2 100 71.3 76.8 74.4 M1.3 M-1-3 I-3 100 72.7 77.7 75.3

TABLE 1b VHR(t)/% @ c(stab.) 100° C., 60 Hz Ex. Mixture Stabiliser /ppm t = 0 h t = 168 h t = 336 h (Ref.) M-1 none 0 80.4 67.1 61.7 C1.1 C-1-1 R-1 100 t.b.d. t.b.d. t.b.d. C1.2 C-1-2 R-2 100 74.1 75.1 69.9 C1.3 C-1-3 R-3 100 73.1 77.9 75.7 M1.1 M-1-1 I-1 100 72.6 81.0 78.8 M1.2 M-1-2 I-2 100 71.3 81.3 80.5 M1.3 M-1-3 I-3 100 72.7 82.2 81.2

TABLE 1c VHR(t)/% @ c(stab.) 60° C., 1 Hz Ex. Mixture Stabiliser /ppm t = 0 h t = 168 h t = 336 h (Ref.) M-1 none 0 88.9 79.4 68.9 C1.1 C-1-1 R-1 100 t.b.d. t.b.d. t.b.d. C1.2 C-1-2 R-2 100 78.2 78.0 70.0 C1.3 C-1-3 R-3 100 78.2 86.2 82.6 M1.1 M-1-1 I-1 100 77.3 90.3 87.6 M1.2 M-1-2 I-2 100 79.7 90.1 89.7 M1.3 M-1-3 I-3 100 78.5 88.1 86.9

TABLE 1d VHR(t)/% @ c(stab.) 60° C., 1 Hz Ex. Mixture Stabiliser /ppm t = 0 h t = 500 h t = 1.000 h (Ref.) M-1 none 0 88.9 73.9 55.5 C1.1 C-1-1 R-1 100 t.b.d. t.b.d. t.b.d. C1.2 C-1-2 R-2 100 78.2 74.5 61.6 C1.3 C-1-3 R-3 100 78.2 87.4 78.2 M1.1 M-1-1 I-1 100 77.3 90.1 82.0 M1.2 M-1-2 I-2 100 79.7 91.4 83.8 M1.3 M-1-3 I-3 100 78.5 89.9 82.7

Examples 2.1.1 to 2.6.3 and Corresponding Comparative Examples

The following mixture (M-2) is prepared and investigated.

Mixture M-2 Composition Compound Concentration No. Abbreviation /% by weight 1 CY-3-O2 12.0 2 CY-3-O4 2.0 3 CY-5-O2 12.0 4 CCY-3-O1 6.0 5 CCY-3-O2 8.0 6 CCY-4-O2 8.0 7 CPY-2-O2 9.0 8 CPY-3-O2 9.0 9 PYP-2-3 5.0 10 CC-3-V1 5.0 11 CC-3-V 19.0 12 CPP-3-2 5.0 Σ 100.0 Physical properties T(N, I) = 86.5° C. n_(e)(20° C., 589 nm) = 1.5924 Δn(20° C., 589 nm) = 0.1092 ε_(⊥)(20°, 1 kHz) = 7.9 Δε(20°, 1 kHz) = −4.2 γ₁(20° C.) = 155 mPa · s k₁₁(20° C.) = 14.6 pN k₃₃(20° C.) = 16.6 pN V₀(20° C.) = 2.08 V

This mixture, mixture M-2, is investigated below with respect to the stability of its voltage holding ratio to irradiation with UV radiation. To this end, this mixture is also divided into several parts.

Firstly, the stability of mixture (M-1) itself is determined. To this end, the stability of mixture M-1 to UV exposure is investigated in a test cell having an appropriate polyimide as alignment material for planar alignment, with a layer thickness of 6.0 μm and flat ITO electrodes. To this end, corresponding test cells are irradiated in the Suntest for 30 min. The voltage holding ratio is then in each case determined after 5 minutes at a temperature of 100° C. The addressing frequency (or measurement frequency) here is 60 Hz, unless indicated otherwise in detail. The results are compiled in Table 2a.

Then, for comparison, 100 ppm, 300 ppm or 600 ppm of the reference compound R-2 are added to three parts of mixture M-2, and the resultant mixtures (C-1.1, C-1.2 and C-1.3.) are investigated as described above. The results are compiled in the following table, Table 2a.

100 ppm, 300 ppm or 600 ppm of in each case one of compounds I-1 to I-3, as indicated above, and of the following compounds I-4 to I-6

are then in each case added to sets of three further parts of mixture M-2, and the stability of the resultant mixtures (C-1.1, C-1.2 and C-1.3, as well as M-1.1, M-1.2 and M-1.3) is investigated as described above. The results are shown in the following tables, Tables 2a and 2b.

TABLE 2a VHR(t)/% @ c(stab.)/ 100° C., 60 Hz Ex. Mixture Stabiliser ppm t = 0 h t = 30 min (Ref.) M-1 none 0 76.2 66.1 C2.1 C-2-1.1 R-2 100 75.6 65.5 C2.2 C-2-1.2 R-2 300 t.b.d. t.b.d. C2.3 C-2-1.3 R-2 600 t.b.d. t.b.d. M2.1.1 M-2-1.1 I-1 100 75.5 65.8 M2.1.2 M-2-1.2 I-1 300 73.6 64.7 M2.1.3 M-2-1.3 I-1 600 69.1 65.1 M2.2.1 M-2-2.1 I-2 100 75.2 68.4 M2.2.2 M-2-2.2 I-2 300 76.2 68.9 M2.2.3 M-2-2.3 I-2 600 73.8 68.9 M2.3.1 M-2-3.1 I-3 100 72.4 73.5 M2.3.2 M-2-3.2 I-3 300 74.9 75.1 M2.3.3 M-2-3.3 I-3 600 72.2 73.4 M2.4.1 M-2-4.1 I-3 100 73.0 73.1 M2.4.2 M-2-4.2 I-4 300 71.0 71.7 M2.4.3 M-2-4.3 I-4 600 71.7 71.1 M2.5.1 M-2-5.1 I-5 100  7.4 72.6 M2.5.2 M-2-5.2 I-5 300 73.1 72.0 M2.5.3 M-2-5.3 I-5 600 72.3 72.2 M2.6.1 M-2-6.1 I-6 100 74.2 73.3 M2.6.2 M-2-6.2 I-6 300 73.1 71.7 M2.6.3 M-2-6.3 I-6 600 t.b.d. t.b.d.

It is readily evident here that compounds I-1 to 1-6 exhibit clearly stabilising properties, even in relatively low concentrations.

The investigations described above are repeated at a temperature of 60° C. and an addressing/measurement frequency of 10 Hz. The results are compiled in the following table, Table 2b.

TABLE 2b VHR(t)/% @ c(stab.)/ 100° C., 60 Hz Ex. Mixture Stabiliser ppm t = 0 h t = 30 min (Ref.) M-1 none 0 90.7 71.7 C2.1 C-2-1.1 R-2 100 84.1 75.2 C2.2 C-2-1.2 R-2 300 t.b.d. t.b.d. C2.3 C-2-1.3 R-2 600 t.b.d. t.b.d. M2.1.1 M-2-1.1 I-1 100 86.4 82.1 M2.1.2 M-2-1.2 I-1 300 85.7 83.8 M2.1.3 M-2-1.3 I-1 600 85.1 79.7 M2.2.1 M-2-2.1 I-2 100 84.2 81.4 M2.2.2 M-2-2.2 I-2 300 83.6 80.9 M2.2.3 M-2-2.3 I-2 600 83.9 80.3 M2.3.1 M-2-3.1 I-3 100 81.7 82.1 M2.3.2 M-2-3.2 I-3 300 83.0 81.5 M2.3.3 M-2-3.3 I-3 600 77.1 80.9 M2.4.1 M-2-4.1 I-3 100 81.9  81.23 M2.4.2 M-2-4.2 I-4 300 77.3 76.4 M2.4.3 M-2-4.3 I-4 600 76.9 77.1 M2.5.1 M-2-5.1 I-5 100 92.3 83.5 M2.5.2 M-2-5.2 I-5 300 84.0 81.5 M2.5.3 M-2-5.3 I-5 600 86.2 79.6 M2.6.1 M-2-6.1 I-6 100 86.6 82.8 M2.6.2 M-2-6.2 I-6 300 88.2 81.5 M2.6.3 M-2-6.3 I-6 600 t.b.d. t.b.d.

Example 3

The following mixture (M-3) is prepared and investigated.

Mixture M-3 Composition Compound Concentration No. Abbreviation /% by weight 1 B-2O-O5 4.0 2 CY-3-O2 10.0 3 CY-5-O2 1.5 4 CCY-3-O2 10.0 5 CCY-5-O2 7.0 6 CPY-2-O2 10.0 7 CPY-3-O2 10.0 8 PYP-2-3 5.5 9 CC-3-V 32.0 10 CC-3-V1 10.0 Σ 100.0 Physical properties T(N, I) 85.0° C. n_(e)(20° C., 589 nm) = 1.5868 Δn(20° C., 589 nm) = 0.1047 ε_(⊥)(20°, 1 kHz) = 6.9 Δε(20°, 1 kHz) = −3.4 γ₁(20° C.) = 108 mPa · s k₁₁(20° C.) = 14.6 pN k₃₃(20° C.) = 17.4 pN V₀(20° C.) = t.b.d. V V₁₀(20° C.) = t.b.d. V

As described in Examples 1 and 2, mixture M-3 is also divided into several parts and its stability to exposure to an LCD backlight and to a UV source is investigated as such and with various added compounds in a test cell with an alignment material for planar alignment and flat ITO electrodes.

Example 4

The following mixture (M-4) is prepared and investigated.

Mixture M-4 Composition Compound Concentration No. Abbreviation /% by weight 1 CY-3-O2 12.0 2 CY-5-O2 10.5 3 CCY-3-O1 6.0 4 CCY-3-O2 7.0 5 CCY-5-O2 5.0 6 CPY-2-O2 12.0 7 CPY-3-O2 12.0 8 PYP-2-3 7.5 9 CC-3-V1 4.0 10 CC-3-V 24.0 Σ 100.0 Physical properties T(N, I) 85.0° C. n_(e)(20° C., 589 nm) = 1.5956 Δn(20° C., 589 nm) = 0.1120 ε_(⊥)(20°, 1 kHz) = 7.9 Δε(20°, 1 kHz) = −4.2 γ₁(20° C.) = 145 mPa · s k₁₁(20° C.) = 14.2 pN k₃₃(20° C.) = 16.7 pN V₀(20° C.) = 2.08 V

As described in Examples 1 and 2, mixture M-4 is also divided into several parts and its stability to exposure to an LCD backlight and to a UV source is investigated as such and with various added compounds in a test cell with an alignment material for planar alignment and flat ITO electrodes.

Example 5

The following mixture (M-5) is prepared and investigated.

Mixture M-5 Composition Compound Concentration No. Abbreviation /% by weight 1 B-2O-O5 4.0 2 CY-3-O2 12.0 3 CCH-34 2.5 4 CCP-V-1 1.5 5 CCY-3-O2 10.0 6 CCY-5-O2 2.0 7 CLY-3-O2 8.0 8 CPY-2-O2 6.0 9 CPY-3-O2 10.0 10 PGIY-2-O4 4.0 11 CC-3-V 30.0 12 CC-3-V1 10.0 Σ 100.0 Physical properties T(N, I) 87.0° C. n_(e)(20° C., 589 nm) = 1.5829 Δn(20° C., 589 nm) = 0.1019 ε_(⊥)(20°, 1 kHz) = 7.1 Δε(20°, 1 kHz) = −3.7 γ₁(20° C.) = 112 mPa · s k₁₁(20° C.) = 15.2 pN k₃₃(20° C.) = 18.0 pN

As described in Examples 1 and 2, mixture M-5 is also divided into several parts and its stability to exposure to an LCD backlight and to a UV source is investigated as such and with various added compounds in a test cell with an alignment material for planar alignment and flat ITO electrodes. 

1. A liquid-crystalline medium, comprising a) one or more compounds of the formula I

in which R¹¹ on each occurrence, independently of one another, denotes H, F, a straight-chain or branched alkyl chain having 1-20 C atoms, in which one —CH₂— group or, if present, a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, and one or, if present, a plurality of —CH₂— groups may be replaced by —CH═CH— or —C≡C—, and in which one H atom or a plurality of H atoms may be replaced by F, OR¹³, N(R¹³)(R¹⁴) or R¹⁵, R¹² on each occurrence, independently of one another, denotes H, a straight-chain or branched alkyl chain having 1-20 C atoms, in which one —CH₂— group or a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, a hydrocarbon radical which contains a cycloalkyl or alkylcycloalkyl unit and in which one —CH₂— group or a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, and in which one H atom or a plurality of H atoms may be replaced by F, OR¹³, N(R¹³)(R¹⁴) or R¹⁵, or an aromatic or heteroaromatic hydrocarbon radical, in which one H atom or a plurality of H atoms may be replaced by OR¹³, N(R¹³)(R¹⁴) or R¹⁵, R¹³ on each occurrence, independently of one another, denotes H, a straight-chain or branched alkyl or acyl group having 1 to 10 C atoms or an aromatic hydrocarbon or carboxylic acid radical having 6-12 C atoms, R¹⁴ on each occurrence, independently of one another, denotes H, a straight-chain or branched alkyl or acyl group having 1 to 10 C atoms or an aromatic hydrocarbon or carboxylic acid radical having 6-12 C atoms, R¹⁵ on each occurrence, independently of one another, denotes a straight-chain or branched alkyl group having 1 to 10 C atoms, in which one —CH₂— group or a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, S¹¹ and S¹² on each occurrence, independently of one another, denote an alkylene group having 1 to 20 C atoms, in which one —CH₂— group or, if present, a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, and in which one H atom or a plurality of H atoms may be replaced by F, OR¹³, N(R¹³)(R¹⁴) or R¹⁵, or denote a single bond, Y¹¹ to Y¹⁴ each, independently of one another, denote methyl or ethyl, Z¹¹ to Z¹⁴ on each occurrence, independently of one another, denote —O—, —(C═O)—, —O—(C═O)—, —(C═O)—O—, —O—(C═O)—O—, —(N—R¹³)—, or —N—R¹³—(C═O)—, or additionally a single bond if S¹¹ is a single bond, provided that both Z¹¹ and Z¹² do not simultaneously denote —O—, and, provided that, if S¹² is a single bond, both Z¹³ and Z¹⁴ do not simultaneously denote —O—, and, provided that if —X¹¹[—R¹¹]_(o)— is a single bond, both Z¹² and Z¹³ do not simultaneously denote —O—, X¹¹ denotes C, O^(•) denotes an oxide radical, p denotes 1 or 2, o denotes (3-p), and, if p is 2, n denotes an integer from 2 to 4, and m denotes (4-n), and, if p is 1, n denotes an integer from 3 to 10, and m denotes (10-n), and

denotes an organic radical having (m+n) bonding sites, and where, in the case where p=1, —X¹¹[—R¹¹]_(o)— may alternatively also denote a single bond, and one or more further compounds selected from: b) one or more compounds of the formula II

in which R²¹ denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkenyl radical having 2 to 7 C atoms and R²² denotes an unsubstituted alkenyl radical having 2 to 7 C atoms, and/or c) one or more compounds selected from the group of the compounds of the formulae III-1 to III-4 and B,

in which R³¹ denotes an unsubstituted alkyl radical having 1 to 7 C atoms, R³² denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, m, n and o each, independently of one another, denote 0 or 1, R^(B1) and R^(B2) each, independently of one another, denote an unsubstituted alkyl radical, alkoxy radical, oxaalkyl radical or alkoxyalkyl radical having 1 to 7 C atoms, or an alkenyl radical or alkenyloxy radical having 2 to 7 C atoms, and L^(B1) and L^(B2) each, independently of one another, denote F or Cl.
 2. Medium according to claim 1, wherein the total concentration of the compounds of the formula I in the medium as a whole is 1 ppm or more to 2000 ppm or less.
 3. Medium according to claim 1, which comprises a compound of the formula II in which R²¹ denotes n-propyl and R²² denotes vinyl.
 4. Medium according to claim 3, wherein the total concentration of the compounds of the formula II in the medium as a whole is from 25% to 45%.
 5. Medium according to claim 1, which comprises one or more compounds of the formula B.
 6. Medium according to claim 1, which comprises one or more compounds of the formula III-4.
 7. Medium according to claim 1, which additionally comprises one or more chiral compounds.
 8. A compound of the formula I

in which R¹¹ on each occurrence, independently of one another, denotes H, F, a straight-chain or branched alkyl chain having 1-20 C atoms, in which one —CH₂— group or, if present, a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, and one or, if present, a plurality of —CH₂— groups may be replaced by —CH═CH— or —C≡C—, and in which one H atom or a plurality of H atoms may be replaced by F, OR¹³, N(R¹³)(R¹⁴) or R¹⁵, R¹² on each occurrence, independently of one another, denotes H, a straight-chain or branched alkyl chain having 1-20 C atoms, in which one —CH₂— group or a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, a hydrocarbon radical which contains a cycloalkyl or alkylcycloalkyl unit and in which one —CH₂— group or a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, and in which one H atom or a plurality of H atoms may be replaced by F, OR¹³, N(R¹³)(R¹⁴) or R¹⁵, or an aromatic or heteroaromatic hydrocarbon radical, in which one H atom or a plurality of H atoms may be replaced by OR¹³, N(R¹³)(R¹⁴) or R¹⁵, R¹³ on each occurrence, independently of one another, denotes a straight-chain or branched alkyl or acyl group having 1 to 10 C atoms or an aromatic hydrocarbon or carboxylic acid radical having 6-12 C atoms, R¹⁴ on each occurrence, independently of one another, denotes a straight-chain or branched alkyl or acyl group having 1 to 10 C atoms or an aromatic hydrocarbon or carboxylic acid radical having 6-12 C atoms, R¹⁵ on each occurrence, independently of one another, denotes a straight-chain or branched alkyl group having 1 to 10 C atoms, in which one —CH₂— group or a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, S¹¹ and S¹² on each occurrence, independently of one another, denote an alkylene group having 1 to 20 C atoms, in which one —CH₂— group or, if present, a plurality of —CH₂— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH₂— groups cannot be replaced by —O—, and in which one H atom or a plurality of H atoms may be replaced by F, OR¹³, N(R¹³)(R¹⁴) or R¹⁵, or denote a single bond, Y¹¹ to Y¹⁴ each, independently of one another, denote methyl or ethyl, Z¹¹ to Z¹⁴ on each occurrence, independently of one another, denote —O—, —(C═O)—, —O—(C═O)—, —(C═O)—O—, —O—(C═O)—O—, —(N—R¹³)—, or —N—R¹³—(C═O)—, or additionally a single bond if S¹¹ is a single bond, provided that both Z¹¹ and Z¹² do not simultaneously denote —O—, and, provided that, if S¹² is a single bond, both Z¹³ and Z¹⁴ do not simultaneously denote —O—, and, provided that if —X¹¹[—R¹¹]_(o)— is a single bond, both Z¹² and Z¹³ do not simultaneously denote —O—, X¹¹ denotes C, p denotes 1 or 2, o denotes (3-p), and, if p is 2, n denotes an integer from 2 to 4, and m denotes (4-n), and, if p is 1, n denotes an integer from 3 to 10, and m denotes (10-n), and

denotes an organic radical having (m+n) bonding sites, and where, in the case where p=1, —X¹¹[—R¹¹]_(o)— may alternatively also denote a single bond.
 9. Compound of the formula I according to claim 8 in which p denotes
 2. 10. Compound of the formula I according to claim 9, selected from the group of the compounds of the formulae I-1 to I-9:


11. Electro-optical display or electro-optical component, which contains a liquid-crystalline medium according to claim
 1. 12. Display according to claim 11, which is based on the IPS, FFS, VA or ECB effect.
 13. Display according to claim 11, which contains an active-matrix addressing device.
 14. Process for the preparation of a liquid-crystalline medium according to claim 1, comprising mixing one or more compounds of the formula I with one or more compounds of the formula II and/or one or more compounds selected from the group of the compounds of the formulae III-1 to III-4 or formula B.
 15. Process for the stabilisation of a liquid-crystalline medium, which comprises providing one or more compounds of the formula I of claim 1, and optionally one or more compounds selected from the group of the compounds of the formulae OH-1 to OH-6,

to the medium.
 16. Process for the preparation of a compound of the formula I according to claim 8, comprising reacting an alcohol containing two 1-oxy-2,2,6,6-tetramethylpiperidin-4-yl groups with a derivatised ring structure that will provide a compound of the formula I, such as, for example, a dicarboxylic acid dihalide or a tetracarboxylic acid tetrahalide.
 17. The process of claim 16, wherein the derivatised ring structure has dicarboxylic acid dihalide or a tetracarboxylic acid tetrahalide derivatisation.
 18. The medium of claim 1, wherein, in formula I, either: p=1 and n denotes 2 or 3, or p=2 and n denotes an integer from 4 to
 8. 19. The compound of claim 8, wherein, in formula I, either: p=1 and n denotes 2 or 3, or p=2 and n denotes an integer from 4 to
 8. 